KDE Plasma 5 missing icons after using GNOME desktop environment?

I've run into this problem 3-4 times now and I'm wondering if someone knows the real cause. I suspect it comes down to one file, but I haven't isolated it yet.

KDE Plasma operates normally, until I log into GNOME and then back into KDE Plasma. Once returning to KDE Plasma most of the Application Launcher, Task Manager Panel, and Dolphin Icons are missing.

My steps to reproduce this are:

• Create a new test user account, account type: admin
• Log into the KDE Plasma Desktop environment
• Log out of KDE Plasma
• Log into GNOME (on Xorg)
• Log out of GNOME
• Log back into KDE Plasma
• Most icons are missing, as shown in this screenshot

One of the joys of Linux is the freedom to switch between Window Managers. Heck, you can even be running two window managers at the same time with startx -- :2 and CTRL + ALT + F7 / CTRL + ALT + F1 to toggle between them, so kind of frustrated that switching to GNOME and back isn't working quite so smooth for me.

System Details:

OS: Ubuntu 21.10 x86_64 
Kernel: 5.13.0-22-generic 
DE: Plasma 5.22.5 
WM: KWin 

UPDATE: One strange observation, even after removing ALL file in /home/test and logging back into KDE Plasma, the icons are still missing. Previously when this happened, I fixed it by creating a new user account and moving all my files to the new user account, but it seems the problem may be outside of /home/...

Finally, I have got the solution for this, and it's quite painless. If I hit this a few more times, maybe I can find a more precise solution, but for now this should fix it for you.

Basically, just delete all of the tmp files and reboot.

sudo find /tmp/ /var/tmp/ -mindepth 1 -delete
sudo reboot

It's almost certainly possible to further narrow this down to THE TMP FILE(s) that's causing the problem, and to skip rebooting perhaps via sudo systemctl restart ssdm or similar, but this is so much better than fruitlessly rebuilding my home directory again...