Add-in taskpane suddenly opens up blank while add-in code is still normally running

[k-bu]

Since 2-3 weeks web add-ins disappear in Excel, PowerPoint and Word, although the add-in code hasn't changed at all. If I open the console via "Attach debugger" then I see the log from the add-in, as if everything were normal. Its code gets fully executed, but the opened taskpane stays empty, also without context menu.

Your Environment

• Platform: PC desktop
• Host: Microsoft® Word for Microsoft 365 MSO (Version 2601 Build 16.0.19628.20204) 64-bit
• Operating System: Windows 11
• WebView2 runtime: 144.0.3719.115

Provide additional details

Two workarounds help restoring the add-in's taskpane:
a) Close the Office applications, then delete "%LOCALAPPDATA%/Microsoft/Office/16.0/Wef" and then restart Office.
b) Terminate the "msedgewebview2.exe" instance, that is shared between all Office applications, via task manager. The instance is auto restarted and immediately also shows our add-in. No restart of the Office application required.

Useful logs

No Javascript or network errors in the console at all.

[github-actions]

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[k-bu]

Additional info resp. a 3rd workaround:

1. Drag the task pane window from the default right side to a floating state.
2. Drag it back, thus dock it back to the right side.
3. The task pane is visible again (although this workaround does not always work)

[k-bu]

Meanwhile I also tried using an older WebView2 runtime version, by setting the environment variable WEBVIEW2_BROWSER_EXECUTABLE_FOLDER pointing to an unpacked version 142.0.3595.53. I can then see the Word process starting msedgewebview2.exe processes of the old version, but the issue still happens. So it seems that it's no WebView2 runtime issue, but an Office(API) issue.

I think I also have to mention that the add-in immediately opens a login dialog via Office.context.ui.displayDialogAsync. It seems as if the main addin task pane gets rendered and displayed for a very short moment, but then disappears when the dialog window is displayed. The dialog window always correctly displays its content, but the content of the main addin task pane is already blank.

[k-bu]

I was able to narrow down the problem a little further. As already mentioned above, we're displaying a login dialog. But we're also "restoring" the add-in's task pane width. When the width of the task pane is changed, then we store it in the browser's local storage and restore it immediately in the Office.onReady() handler when the add-in is opened the next time. We do this, because the default width is to small for our use cases. So immediately resizing the task pane width on startup seems to be a problem in Office/app. I inserted a workaround by a simple sleep and the problem seems to be gone by that:

                    misc.sleep(100).then(() => {
                        Office.extensionLifeCycle.taskpane.setWidth(previousWidth).catch((error) => {
                            log.error(error);
                        });
                    });

[Dykam]

Fascinating, we are getting reports of our addin failing to display after dragging it out of the UI or the opposite. I suspect it has the same root cause, as for you it appears to be a workaround to fix the problem.

One workaround for us is to simply close (X) the addin and reopen. If that doesn't work for you, it might be a different problem.

[k-bu]

If that doesn't work for you, it might be a different problem.

No, unfortunately that doesn't help with our problem.

[davidchesnut]

Hi k-bu and Mark (@Dykam),

I just want to confirm you're not running into this recent change we made where showAsTaskpane no longer opens the task pane for store deployed add-ins. Increased control over Office Add-in user experiences

Thanks!

[k-bu]

I just want to confirm you're not running into this recent change we made where showAsTaskpane no longer opens the task pane for store deployed add-ins. Increased control over Office Add-in user experiences

Thanks for the info. No, I've never even tested the auto open features. Although some users requested it, we've decided to not support it. But while reading the blog post, I realized that I should probably also mention that our add-in also does not use a shared runtime. Perhaps that will also play a role in the end. But in any case, no other add-ins are being used at the same time.

[davidchesnut]

Hi k-bu, okay I understand now. the task pane does open, but it's not rendering at all. It sounds like you are doing some UI activities right after the task pane loads such as setting width and opening a dialog? If you could share a simple sample that repros this issue that would be helpful.

Akshay Dixit (MSFT) (@kustonaut) can you please help investigate this issue? Thanks!