[palosanto]

If you bring up File Explorer, then enter just "Applications" and hit enter, it should give you a full list of installed applications (alternatively, use Windows + R for the run command, and then enter shell:AppsFolder). If you double-click on MobileSheets in the list, does it run the app as you would expect? Is it only the taskbar that causes the issue?

Thanks,
Mike

Yes it runs fine, like I said it's only the taskbar. 
I also went to Appdata>Roaming>Microsoft>Internet Explorer>Quick Launch>User Pinned>Taskbar and all apps shown in the taskbar are there except MSP even though the icon is in the taskbar.
Oh well nevermind, I hate to waste your time, but on the other hand it must have something to do with this app because it's the only one behaving like that ...
I also noticed that after logging off or restarting, the MSP icon changes to a blue monitor icon.

EDIT:  I tried running MSP with windows in Safe Mode and although it doesn't actually starts, a white window appears it seems to want to load for a few seconds and it doesn't take me to the file explorer like before.  The same window appears if I launch the app from windows start so it looks like the taskbar instance would work normally but I guess the program won't launch from Safe mode.
It looks like there is some app or service loaded in the background somehow creates the problem when Windows is in normal mode