I have not added any new services or processes or software since the last time I did the reinstall and the problem didn't resurface until the 26th. (That's about 3 and 1/2 days before it resurfaced.)
You're asking me to do a typical Windows clean boot where I would have to turn off all non-Microsoft services and reboot, and then see if the problem resurfaces, by attempting to restart all those services one at a time.
I'm happy to help, I don't have the time available to do all that. The problem is sporadic and is not easily repeatable,
Note that I have 23 different non-Microsoft services that are enabled and running and 12 more that are disabled (and not running). No new hardware or software components have been added, and only a one or two software apps (such as Edge, Chrome, Malwarebytes, and PDF Exchange editor) have been updated.
The menu has a background .jpg image and that is set at about 30% transparency. I think the problem lies directly with Start 11's drawing of the menu background image. As you can see by the samples that drawing of the background image shows on the left side for about 80% of the way (left to right) with no background menu image continuing onto (under?) the remaining 20% to the right. The transparency is working on both left and right sides.