I have also encountered this bug with 455.22.04 (beta Vulkan driver). I was not running Chrome, but I was running Firefox 81.0. In the background there was a video encoding process running (ffmpeg, purely CPU-based). There was Ktorrent running, seeding a number of torrents, so there was some IO activity. I was also on a Skype call (using the official Skype client app), the call was audio-only. There was enough free RAM, as I remember, maybe 6-8 GiB or so.
I could not collect nvidia-bug-report while the error was happening as nvidia-bug-report.sh would hang; I collected the report immediately after a hard reboot. I’ve also attached kernel log, where you can see the error at the end. There are also page allocation errors before that (which was reported here: 455.23.04: Page allocation failure in kernel module at random points), but that happened some time before the null pointer bug, so it might not be related.
nvidia-bug-report.log.gz (266.7 KB)
kern.log (196.1 KB)