In Bookworm I no longer see the "lock reclaim failed" errors. Further investigation revealed that the affected installations were also affected by five-second delays as described here <https://lore.kernel.org/linux-nfs/59682160-a246-395a-9486-9bbf11686...@mathematik.uni-wuerzburg.de/>. These show similar symptoms and they also occur on nfs v4.{1,2} only.
So I had to change the lines in <etc/exports> from | /srv/nfs gss/krb5p(rw,fsid=0,crossmnt,no_subtree_check) to | /srv/nfs *(sec=krb5p,rw,fsid=0,crossmnt,no_subtree_check) Done that and everything runs fine. In my experience the bug report can be closed.
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