Hi, Jürgen, Thank you for posting this! I also observe that the bug affects nfs-client on 5.10 kernel nfs-server is not affected (works with both 5.9 and 5.10 kernels)
I followed your suggestions, but unfortunately with no luck. I tried adding principles and building the latest nfs-utils. But downgrading to 5.9 kernel helped! Thanks again Best regards, Albert