Mount failed with "NFS: nfs4_discover_server_trunking unhandled error -22" - any suggestions?
Irritatingly I have just found a solution, I did run the search again with the full error message and found
https://bbs.archlinux.org/viewtopic.php?id=204532
and at the end the relevant advice to change the mount command to
mount -t nfs -o nolock,posix,nfsvers=3 ...
Obviously NFS has been updated and the Synology box hasn't (I might look at whether there are any updates for it)
I have tried the fix and it works here
I was debating whether to delete the question but as it applied to 18.04 it may be relevant to others and may be easier to find here.
Hope it is of use
graham