Deleting jupyter session displays error message related to websocket connection

[vambavaram]

Environment data

• VS Code version: 1.101.1
• Jupyter Extension version (available under the Extensions sidebar): 2025.3.0
• Python Extension version (available under the Extensions sidebar): 2025.8.0
• OS (Windows | Mac | Linux distro) and version: Windows
• Python and/or Anaconda version:
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): N/A
• Jupyter server running: Remote

Expected behaviour

1. Delete jupyter session (kernel also gets deleted)
2. websocket connection is disposed
3. run a cell
4. new session, kernel connection, websocket connection created

Actual behaviour

Jupyter session is deleted and kernel disposed. An error notification pops up in the extension. Internally there is a 404 thrown since the corresponding websocket connection is not found. We want to prevent this error from happening.

Steps to reproduce:

1. api call: DELETE api/sessions/{sessionId} to delete the session.
2. error thrown

Screenshot of error

Logs

Output for Jupyter in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Jupyter)

Visual Studio Code (1.101.1, undefined, desktop)
Jupyter Extension Version: 2025.3.0.
Python Extension Version: 2025.8.0.
Pylance Extension Version: 2025.6.1.
Platform: win32 (x64).
Home = c:\Users\vambavaram
Temp Storage folder ~\AppData\Roaming\Code\User\globalStorage\ms-toolsai.jupyter\version-2025.3.0
No workspace folder opened.
03:13:25.794 [info] Starting Kernel (MSGLarge (16 vcores/112g - 4 executors) [Untitled-2]) for 'Untitled-2.ipynb' (disableUI=false)
03:14:00.109 [info] https://australiaeast.api.securityplatform.microsoft.com/spark-notebook/interactive: Kernel started: 281b8d17-31ec-4986-b7c9-27567f0f9621
03:14:04.118 [info] Started session for kernel startUsingRemoteKernelSpec:fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark
03:14:04.137 [warn] Unhandled message found: kernel_info_reply
03:14:04.139 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:14:04.196 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:14:04.199 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:14:04.449 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:14:04.451 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:18:38.690 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:22.560 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:22.718 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:54.905 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:55.193 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:55.201 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:55.455 [info] Kernel successfully started
03:19:55.466 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:55.580 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:19:55.903 [error] Widget Error: Failed to access CDN https://unpkg.com/ after 0 attempt(s), TypeError: Failed to fetch
03:19:56.312 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:21:34.189 [error] Exception while handling messages: SyntaxError: Unexpected end of JSON input
03:21:34.916 [error] Error in websocket: (404) Not Found, undefined, Headers = {"date":"Wed, 25 Jun 2025 10:21:34 GMT","transfer-encoding":"chunked","connection":"keep-alive","access-control-allow-origin":"*","access-control-expose-headers":"Azure-AsyncOperation,Operation-Location,x-ms-request-id,ETag","strict-transport-security":"max-age=31536000; includeSubDomains","x-ms-correlation-request-id":"98994851-787f-4b23-a93c-55469d25e672","x-azure-ref":"20250625T102134Z-177796b878bdxb8ghC1YVR4bag00000012ag000000003qrn","x-cache":"CONFIG_NOCACHE"}
03:21:34.917 [error] Error in websocket Error: Unexpected server response: 404
    at ClientRequest.<anonymous> (c:\Users\~\vscode-trident-fork\extensions\desktop\dist\extension\extension.js:904:7)
    at ClientRequest.emit (node:events:530:35)
    at HTTPParser.parserOnIncomingClient [as onIncoming] (node:_http_client:716:27)
    at HTTPParser.parserOnHeadersComplete (node:_http_common:117:17)
    at TLSSocket.socketOnData (node:_http_client:558:22)
    at TLSSocket.emit (node:events:518:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at TLSSocket.Readable.push (node:internal/streams/readable:392:5)
    at TLSWrap.onStreamRead (node:internal/stream_base_commons:189:23)
    at TLSWrap.callbackTrampoline (node:internal/async_hooks:130:17)
03:21:34.922 [info] Dispose Kernel 'Untitled-2.ipynb' associated with 'Untitled-2.ipynb'

[DonJayamanne]

Please could you enable logging as follows:

• Open settings & go into Jupyter->Logging
• Change the value to trace
• Reload VS Code,
• Attempt to repro the issue & then copy the output from the Jupyter output panel (use the command Jupyter: Show Output to get to the logs).

[DonJayamanne]

Also please can you install the latest version of the Jupyter extension

[vambavaram]

done @DonJayamanne

Visual Studio Code (1.101.1, undefined, desktop)
Jupyter Extension Version: 2025.5.0.
Python Extension Version: 2025.8.0.
Python Environment Extension not installed.
Pylance Extension Version: 2025.6.1.
Platform: win32 (x64).
Home = c:\Users\vambavaram
Temp Storage folder ~\AppData\Roaming\Code\User\globalStorage\ms-toolsai.jupyter\version-2025.5.0
No workspace folder opened.
03:49:00.351 [debug] Start refreshing Kernel Picker (1750848540351)
03:49:00.395 [debug] Get Custom Env Variables, Class name = Qm, completed in 45ms, has a truthy return value, Arg 1: undefined, Arg 2: "RunPythonCode"
03:49:00.395 [debug] Jupyter Paths kernels: 
03:49:00.405 [debug] Kernel Spec Root Paths, ~\AppData\Roaming\jupyter\kernels, c:\ProgramData\jupyter\kernels
03:49:00.408 [trace] Preferred Remote kernel for Untitled-2.ipynb is 281b8d17-31ec-4986-b7c9-27567f0f9621
03:49:00.409 [info] Deleting old temp dir ~\AppData\Roaming\Code\User\globalStorage\ms-toolsai.jupyter\version-2025.3.0
03:49:00.410 [debug] End refreshing Kernel Picker (1750848540351)
03:49:00.857 [trace] Search for KernelSpecs in Interpreter c:\Python313\python.exe
03:49:00.858 [debug] Start refreshing Kernel Picker (1750848540858)
03:49:01.416 [debug] End refreshing Kernel Picker (1750848540858)
03:49:01.838 [trace] Conda file is conda
03:49:03.705 [debug] Start refreshing Kernel Picker (1750848543705)
03:49:03.709 [trace] Preferred Remote kernel for Untitled-2.ipynb is 281b8d17-31ec-4986-b7c9-27567f0f9621
03:49:12.221 [trace] Disposing Jupyter Lab Helper
03:49:12.221 [trace] SessionManager - dispose contents manager
03:49:12.221 [trace] ShutdownSessionAndConnection - dispose session manager
03:49:12.222 [trace] Finished disposing Jupyter Lab Helper
03:49:12.222 [trace] UniversalRemoteKernelFinder: Writing 3 remote kernel connection metadata to cache
03:49:12.242 [debug] End refreshing Kernel Picker (1750848543705)
03:49:32.431 [trace] Preferred Remote kernel for Untitled-2.ipynb is 281b8d17-31ec-4986-b7c9-27567f0f9621
03:49:33.880 [debug] Handle Execution of Cells 0 for Untitled-2.ipynb
03:49:33.881 [trace] Execute Notebook Untitled-2.ipynb. Step 1
03:49:33.881 [trace] Connect to Kernel Untitled-2.ipynb. Step 2
03:49:33.882 [debug] start the kernel, options.disableUI=false for Untitled-2.ipynb
03:49:33.884 [info] Starting Kernel (MSGLarge (16 vcores/112g - 4 executors) [Untitled-2]) for 'Untitled-2.ipynb' (disableUI=false)
03:49:33.889 [debug] KernelProvider switched kernel to id = fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark
03:49:33.895 [trace] Registering commtarget jupyter.widget
03:49:33.896 [debug] Controller selection change completed
03:49:35.591 [trace] createNewKernelSession fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark
03:50:25.252 [info] https://australiaeast.api.securityplatform.microsoft.com/spark-notebook/interactive: Kernel started: 8df13778-85ec-4b62-a390-99f9984d1a0c
03:50:25.253 [trace] Waiting for idle on (kernel): 8df13778-85ec-4b62-a390-99f9984d1a0c -> unknown
03:50:27.584 [trace] Got status idle in waitForIdleOnSession
03:50:27.584 [trace] Finished waiting for idle on (kernel): 8df13778-85ec-4b62-a390-99f9984d1a0c -> idle
03:50:27.585 [info] Started session for kernel startUsingRemoteKernelSpec:fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark
03:50:27.586 [trace] Started running kernel initialization for Untitled-2.ipynb
03:50:27.586 [trace] Executing silently Code (idle) = try:\nimport ipywidgets as _VSCODE_ipywidgets\nprint("e976ee50-99ed-4aba-9b6b-9dcd5634d07d:IPy
03:50:27.600 [warn] Unhandled message found: kernel_info_reply
03:50:27.608 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:50:27.678 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:50:27.681 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:50:27.880 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:50:27.882 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:54:40.194 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:55:36.239 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:55:40.526 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:20.723 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:24.614 [trace] Executing silently Code (completed) = try:\nimport ipywidgets as _VSCODE_ipywidgets\nprint("e976ee50-99ed-4aba-9b6b-9dcd5634d07d:IPy with 2 output(s)
03:56:24.614 [trace] Determined IPyWidgets Version as 8
03:56:24.614 [trace] Version of IPyWidgets 8 determined after 410.719s
03:56:24.615 [trace] Executing silently Code (idle) = def __VSCODE_inject_module():\ndef __VSCODE_call_function(function, callback, data=None):
03:56:24.618 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:24.629 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:24.860 [trace] Executing silently Code (completed) = def __VSCODE_inject_module():\ndef __VSCODE_call_function(function, callback, data=None): with 1 output(s)
03:56:24.861 [debug] Requesting Kernel info
03:56:24.861 [trace] Got Kernel info
03:56:24.862 [trace] End running kernel initialization, now waiting for idle
03:56:24.862 [trace] Waiting for idle on (kernel): 8df13778-85ec-4b62-a390-99f9984d1a0c -> idle
03:56:24.863 [trace] Finished waiting for idle on (kernel): 8df13778-85ec-4b62-a390-99f9984d1a0c -> idle
03:56:24.863 [trace] End running kernel initialization, session is idle
03:56:24.864 [debug] Updating preferred kernel for remote notebook 8df13778-85ec-4b62-a390-99f9984d1a0c
03:56:24.865 [trace] Registering Kernel Completion Provider from kernel MSGLarge (16 vcores/112g - 4 executors) [Untitled-2] for language python
03:56:24.865 [debug] Start refreshing Kernel Picker (1750848984865)
03:56:24.867 [trace] IPyWidgetScriptSource.initialize
03:56:24.867 [info] Kernel successfully started
03:56:24.872 [trace] Executing silently Code (idle) = import os as _VSCODE_os\nimport sys as _VSCODE_sys\nimport builtins as _VSCODE_builtins\nif _VSCODE_o
03:56:24.873 [trace] Connected to Kernel Untitled-2.ipynb. Step 3
03:56:24.874 [trace] executeCell 0. Step 4
03:56:24.876 [trace] Cell Index:0 sent to kernel
03:56:24.882 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:24.894 [trace] Storing Preferred remote kernel for Untitled-2.ipynb is 8df13778-85ec-4b62-a390-99f9984d1a0c
03:56:24.909 [trace] Executing silently Code (idle) = # Copyright (c) Microsoft Corporation. All rights reserved.\n# Licensed under the MIT License.\n#
03:56:24.990 [trace] Start cell 0 execution @ 1750848984990 (clear output)
03:56:24.991 [debug] Kernel acknowledged execution of cell 0 @ 1750848984990
03:56:24.995 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:25.152 [trace] Web view is ready to receive widget messages
03:56:25.157 [trace] Widget Message: Received IPyWidgets_kernelOptions in ScriptManager
03:56:25.160 [trace] Widget Message: Received IPyWidgetMessages.IPyWidgets_kernelOptions
03:56:25.167 [trace] Widget Message: data-base-url set to https://australiaeast.api.securityplatform.microsoft.com/spark-notebook/interactive
03:56:25.173 [trace] Widget Message: Received IPyWidgets_kernelOptions in ScriptManager
03:56:25.174 [trace] Widget Message: Received IPyWidgetMessages.IPyWidgets_kernelOptions
03:56:25.174 [trace] Widget Message: data-base-url set to https://australiaeast.api.securityplatform.microsoft.com/spark-notebook/interactive
03:56:25.242 [trace] Executing silently Code (completed) = import os as _VSCODE_os\nimport sys as _VSCODE_sys\nimport builtins as _VSCODE_builtins\nif _VSCODE_o with 1 output(s)
03:56:25.243 [trace] Remote Python Env for Untitled-2.ipynb not determined as exe is empty
03:56:25.311 [error] Widget Error: Failed to access CDN https://unpkg.com/ after 0 attempt(s), TypeError: Failed to fetch
03:56:25.473 [trace] Cell 0 completed in 0.483s (start: 1750848984990, end: 1750848985473)
03:56:25.474 [trace] Cell 0 executed successfully
03:56:25.551 [trace] Start cell 0 execution @ undefined
03:56:25.552 [trace] Cell 0 completed in 1750848985.473s (start: undefined, end: 1750848985473)
03:56:25.709 [trace] Executing silently Code (completed) = # Copyright (c) Microsoft Corporation. All rights reserved.\n# Licensed under the MIT License.\n# with 2 output(s)
03:56:25.714 [error] Exception while handling messages: TypeError: Cannot read properties of null (reading 'msg_type')
03:56:26.828 [trace] Disposing Jupyter Lab Helper
03:56:26.828 [trace] SessionManager - dispose contents manager
03:56:26.828 [trace] ShutdownSessionAndConnection - dispose session manager
03:56:26.829 [trace] Finished disposing Jupyter Lab Helper
03:56:26.829 [trace] UniversalRemoteKernelFinder: Writing 3 remote kernel connection metadata to cache
03:56:26.843 [debug] End refreshing Kernel Picker (1750848984865)
03:56:47.644 [error] Exception while handling messages: SyntaxError: Unexpected end of JSON input
03:56:48.326 [error] Error in websocket: (404) Not Found, undefined, Headers = {"date":"Wed, 25 Jun 2025 10:56:48 GMT","transfer-encoding":"chunked","connection":"keep-alive","access-control-allow-origin":"*","access-control-expose-headers":"Azure-AsyncOperation,Operation-Location,x-ms-request-id,ETag","strict-transport-security":"max-age=31536000; includeSubDomains","x-ms-correlation-request-id":"d213ae1a-e5af-4e6b-bcaa-314264db0ee0","x-azure-ref":"20250625T105647Z-17bf6dd799cjlmnvhC1CO16rqc0000000b9g000000000414","x-cache":"CONFIG_NOCACHE"}
03:56:48.327 [error] Error in websocket Error: Unexpected server response: 404
    at ClientRequest.<anonymous> (~\vscode-trident-fork\extensions\desktop\dist\extension\extension.js:904:7)
    at ClientRequest.emit (node:events:530:35)
    at HTTPParser.parserOnIncomingClient [as onIncoming] (node:_http_client:716:27)
    at HTTPParser.parserOnHeadersComplete (node:_http_common:117:17)
    at TLSSocket.socketOnData (node:_http_client:558:22)
    at TLSSocket.emit (node:events:518:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at TLSSocket.Readable.push (node:internal/streams/readable:392:5)
    at TLSWrap.onStreamRead (node:internal/stream_base_commons:189:23)
    at TLSWrap.callbackTrampoline (node:internal/async_hooks:130:17)
03:56:48.331 [info] Dispose Kernel 'Untitled-2.ipynb' associated with 'Untitled-2.ipynb'
03:56:48.332 [debug] Cancel pending cells
03:56:48.332 [trace] Shutdown session - current session, called from 
         at HT.shutdownImplementation (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:279:34055)
        at HT.dispose (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:279:33046)
        at Ds (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:115:867)
        at e (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:282:32640)
        at i_.dispose (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:282:32885)
        at Uy.onKernelDisconnected (~\.vscode\extensions\ms-toolsai.jupyter-2025.5.0-win32-x64\dist\extension.node.js:282:10550)
03:56:48.332 [debug] shutdownSession 8df13778-85ec-4b62-a390-99f9984d1a0c, fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark - start
03:56:48.332 [debug] Session cannot be shutdown fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark
03:56:48.332 [trace] Disposing Jupyter Lab Helper
03:56:48.332 [trace] SessionManager - dispose contents manager
03:56:48.332 [trace] ShutdownSessionAndConnection - dispose session manager
03:56:48.333 [trace] Shutdown session -- complete
03:56:48.333 [debug] shutdownSession 8df13778-85ec-4b62-a390-99f9984d1a0c, fe3300f06ef1434ddaf691a6f2fe23a183fa5250dc37e17924513b102712d0f8..MSGLarge.python3.\.-m#synapsekernel.synapse_pyspark - shutdown complete
03:56:48.333 [debug] Kernel got disposed, hence there is no longer a kernel associated with Untitled-2.ipynb
03:56:48.335 [trace] Finished disposing Jupyter Lab Helper
03:56:50.340 [debug] Start refreshing Kernel Picker (1750849010340)
03:56:51.869 [trace] Disposing Jupyter Lab Helper
03:56:51.869 [trace] SessionManager - dispose contents manager
03:56:51.869 [trace] ShutdownSessionAndConnection - dispose session manager
03:56:51.870 [trace] Finished disposing Jupyter Lab Helper
03:56:51.870 [trace] UniversalRemoteKernelFinder: Writing 3 remote kernel connection metadata to cache
03:56:51.895 [debug] End refreshing Kernel Picker (1750849010340)