There is an old thread about this issue in the Cubase 9 forum, and the issue still remains in C 10.5, at least for me.
Exactly as the OP described in this thread: https://www.steinberg.net/forums/viewtopic.php?f=250&t=145394
And yes, I’ve read the online manual about audio quantizing and followed it to the letter, just to make sure that I’m doing it the right way, and the procedure has not changed in C 10.5, but still nothing happens when I click Quantize!
I should mention that this is the first time for me that quantizing audio doesn’t work.
I’ve done it many times before with success so I would be very interested if there is something that triggers this odd behaviour!?
BTW, All audio files are 24 bit mono, “musical mode” (if that matters)…