Cinnamon becomes mostly unresponsive after switching users

[juliuspopp]

 * Cinnamon version 4.8.6
   - no daily builds
 * Distribution - Mint 20.1
 * Graphics hardware *and* driver:  Graphics:  Device-1: Intel Xeon E3-1200 v3 Processor Integrated Graphics vendor: ASRock 
           driver: i915 v: kernel bus ID: 00:02.0 chip ID: 8086:041a 
           Display: x11 server: X.Org 1.20.9 driver: modesetting unloaded: fbdev,vesa 
           resolution: 3840x2160~30Hz 
           OpenGL: renderer: Mesa DRI Intel HD Graphics P4600/P4700 (HSW GT2) v: 4.5 Mesa 20.2.6 
           compat-v: 3.0 direct render: Yes 
 * 64 bit
 * Attachments
[syslog.txt](https://github.com/linuxmint/cinnamon/files/6643470/syslog.txt)
[xsession-errors user2.txt](https://github.com/linuxmint/cinnamon/files/6643473/xsession-errors.user2.txt)
[xsession-errors user1.txt](https://github.com/linuxmint/cinnamon/files/6643480/xsession-errors.user1.txt)



**Issue**
Most of the desktop (windows) unresponsive, only panel shows open windows correctly (e.g. when closing a window). Not responding to mouse (e.g. when opening mint menu, keyboard worked, mouse didn't).


**Steps to reproduce**
- do something on user 1 (e.g. have Firefox and Thunderbird editing two emails open)
- switch to user 2 (today: root user), do something, log out
- log in again to user 1, try to send that email. Panel is working, alt+tab also, but the correct window is not displayed after alt-tabbing, neither is a window updated upon clicking on it - most of the desktop appears frozen. Screenshot utility was working.


**Expected behaviour**
Cinnamon works as normal and as is the case without multiple users


**Other information**
FIrst appeared with Linux Mint 20.1, was not there in 20.0.


**Configuration info, if applicable**
- 

[ItzSwirlz]

Are you sure you have all the python3 gtk libraries where they need to be? Because cinnamon-launcher is hinting Gtk is failing to initialize

[leigh123linux]

@ItzSwirlz Gtk fails to initialize when X has crashed.

[juliuspopp]

@ItzSwirlz thanks for the comment, I only now read it, didn't get the notification even though I am subscribed to the issue. Will try to correct my preferences.

Anyway, had the same issue again with Cinnamon 5.0.
Was working with main account, switched to other user, logged out, worked in my account again, and then the bug occurred around 10:37 on Jul 26 when I unsuccessfully tried to switch to Ctrl+Alt+F2 to restart Cinnamon:

Jul 26 10:37:50 julius128 systemd[1]: Started Getty on tty2.

Panel and Alt+Tab view were still working and updating (though right-clicking on the panel to close an application did not work), but the central 95% of the screen were glitchy and did not display the apps.

syslog.txt
dmesg.txt
journalctl.txt
xsession-errors.txt

[gt4w4al]

I have the same issue.
Some details are discussed in this topic : the bug seems linked to Cinnamon and not a linux Mint version.
#10570