My Calibre was installed for years on network storage, and I was accessing from Win machine thru UNC (\
\IP address\Calibre\calibre-portable.exe).
Also when I'm updating version, I'm updating from CMD:
calibre-portable-installer-9.0.0.exe \\IP address\Calibre.
Usually, it recognize it as
update, ask about that and finish everything.

This time, from 8.1.6 to 9.0, no question, only unpacking.
After finishing, I tried to start and get an error.
This application failed to start because no Qt platform plugin could be initialized. Reinstaling application may fix this problem.
Ok, let's try again. Same result.
Ok, let's try different approach, install on local drive, start. Works.
Backup Calibre settings on different location. Copy whole "new" Calibre folder to network location, restore Calibre settings. Not work. Same error.
Any advice?
P.S. Calibre Library is copied to 2 different locations, just for any case.