My app was randomly killing the taskbar which would disappear on app exit and not reappear until you restarted Windows. Sometimes it would flash the taskbar off and on instead.
The culprit? A single window with Menu Bar Visible option set to on. You can only see this option under the gear symbol of the inspector when selecting the window. It wasn’t even necessary to instantiate the window apparently.
If you’re still searching for the problem, the following line of code will also kill the taskbar
dim w as new window
When it should be
dim w as new myWindowName
This is a FYI in case it hits someone else
Xojo 2021 r2.1 Windows 10 Pro (20H2)