Interesting. Unraid OS 6.9.1 is on kernel 5.10.21 and the referenced patch is not applied. Upcoming 6.9.2 release is on kernel 5.10.27 which does have the patch. Working on finalizing the release now.
There is an interesting kernel bug fix, which looks like our case https://lkml.org/lkml/2021/3/29/499
I don't know if this already available in a linux version for Unraid, perhaps @limetech can tell?