NFS links die with garbage files.

For this discussion, I have two machines.  The server is running 15.0p4 and
is serving nfs to a couple dozen machines. The client is 15.0p5 and
mounting a few dozen mounts.  They also run NFSv3 as I have never gotten
around to implementing NIS for my home network.  All filesystems are ZFS.

TLDR;
With very light use, one particular mount watched by rtorrent for new files
and filled by rtorrent with incoming files (that are not, in general, read
in situ) ... fails with one element in the NFS root visible, but not
really.  Shows up in ls, but fails "no such file or directory" for stat.

All of my NFS filesystems are put in /d/<machine>/<share> naming scheme and
soft links pick that up and put them where they go in the local filesystem
(if any).  In this case, the failing filesystem is /d/vr/torrent/in ...
which has a subdirectory watch.

Watch is filled by moving files into it on the client.  This is noticed by
rtorrent which runs on the server (kqueue directory watch) and rtorrent
then fills in the files in the root NFS directory with the torrent data.
When a torrent is finished, it is moved by rtorrent to another ZFS and NFS
filesystem (all local to the server).

umount -f on /d/vr/torrent/in followed by a re-mount fixes the problem.

Since this happens over days, I'm at a bit of a loss as to how to proceed
with diagnosis.