Control: retitle -1 nfs4_reclaim_open_state: Lock reclaim failed For what it's worth, I've seen the same symptoms in jessie (kernel 3.16.36 at the time) and Ubuntu trusty (3.13.0-93). In my experience, NFSv4 in stretch is no worse than in jessie.
Rate-limiting those "Lock reclaim failed!" messages would be useful. I've had to add a filter for them in rsyslog to prevent a DoS on my central logging infrastructure. I don't see them often, but when a client gets stuck it can emit this message *many* times. There is definitely more than one trigger for these. I'm under the impression that network partitioning events generate short bursts of such messages, but this is usually benign and does not require a reboot for recovery. Not sure what causes the more severe incidents (I haven't had one in a while, and my NFS environment is intentionally v4-only). My troubleshooting checklist for the next incident includes echo 1 > /sys/kernel/debug/tracing/events/nfs4_lock_reclaim/enable but I haven't had a chance to put this into practice yet.