Hi,
I've followed your recommendations, and used a third computer. I was able to see the problems until I turned off Enhanced Taskbar.
That you see this on 3 PCs, but no one else does, screams that you have the same 3rd party app \ setting on all three.
If you open Windows Sandbox, install ONLY Start11 on it, do you still see it?
That will eat a license (of your 5 pack) so be sure to uninstall Start11 from the Sandbox before you kill it after testing.
Sean Drohan
Stardock Product Lifecycle Manager