https://bugzilla.kernel.org/show_bug.cgi?id=206225
--- Comment #12 from Christoph Marz (derchiller-foren@online.de) --- Follow-up:
After a dist-upgrade, the error returned. I deleted the video acceleration firmware and it was ok again.
When I installed 5.4.14, there were warnings about possibly missing firmware (the nvidia files from firmware-misc-nonfree), so I reinstalled that package and updated the initramfs (I think I missed that step after purging the package). Furthermore, I removed nouveau.config=cipher=0 since that doesn't seem to be related to the error.
To conclude: When it works, I do a dist-upgrade one day and the error returns. Doing a dist-upgrade a few days after makes it work again. The same holds for kernel upgrades.