NFS via IPv6 between 11.2-REL amd64
boxes failed for directories with more than 45 files or directories.
Small directories worked. It seems to be an issue with
ipv6 fragmentation (?), as can be seen by tcpdump:
17:54:16.855978 IP6 nfs-serv > nfs-client frag (0|1448) 2049 > 709: NFS
reply xid 1536109002 reply ok 1440 readdir
17:54:16.855979 IP6 nfs-serv > nfs-client frag (1448|36)
As soon as the NFS request is sent with fragments, it stalls.
Using TCP or IPv4 for the nfs mount works, UDP fails.
This is very likely caused by #231045. (Assuming you've installed the latest security patches.)
There's a problem with IPv6 fragment reassembly. The fix should go in HEAD soon, and I assume there'll be an EN about it too.
*** This bug has been marked as a duplicate of bug 231045 ***