We do not believe this initial thread post to be a problem caused by Start11, but a problem with the OS icon cache.
This is because the initial post showed the problem on the Taskbar and Start menu, but Start11 did not have the taskbar features at the time so it couldn't be Start11.
The only icon issue we are aware of is for the taskbar only for Start11 1.25 on Windows 11 when you have the enhanced taskbar on and some pinned items may have the wrong icon, but never a blank icon like this. This is cleared up with an explorer restart and is resolved in 1.26 which is coming soon.
Generally speaking if you get an icon like that it is probably a broken cache which is an OS level issue. Windows 11 seems especially prone to this.