https://bugzilla.kernel.org/show_bug.cgi?id=206225
--- Comment #9 from Christoph Marz (derchiller-foren@online.de) --- Well, then this might sound strange:
I purged firmware-misc-nonfree, rebooted, sent the system to sleep and resumed, and the distortion was back.
Instead of reinstalling it, I set nouveau.config=cipher=0 and tested again, and everything is fine. Furthermore, now I can use the firmware for Video Acceleration. Before, I always had distortion after resume with that firmware installed.
So everything seems fine now, but is there any downside in disabling the crypt engine?