Comment # 6 on bug 1137344 from Neil Brown

This is very odd.
The error, -95, is EOPNOTSUPP which seems to suggest that the socket isn't set
up properly.
However it also appears that transmission on the socket sometimes works, else
the code wouldn't have a chance to reply to an NFSv4 callback, as is happening
in the first error.

So it seems like an intermittent problem.  It appears to happen often enough
that NFS mounts are not usable, but it doesn't affect every single packet.

What sort of network interface do you have?  Is there anything unusual about it
at all?

Can you please enable rpc debugging, then attempt the mount, then report the
contents of the logs.
To enable rpc debugging use
   rpcdebug -m rpc -s all

use "rpcdebug -m rpc -c all" to disable it again.

Messages appear in the kernel logs and can be collected with
   dmesg > /tmp/log-file

Thanks.