We are running 9.1P2. we have been facing the same issue intermittently. there seems to be a bug that hits the filer port.
here is the BUG detail:
https://mysupport.netapp.com/NOW/cgi-bin/bol?Type=Detail&Display=1141614
To resolve the NFSv4 store pool exhaus issue, we can first try to migrate the LIF that is affected to another node. if that doesn;t resolve try rebooting the server and if the locks are still in pending-delete state, we might need to reboot the node.
you can get the details of the servers causing the higest number of NFSv4 locsk with the help of below commsnd.
ssh admin@node-that-impacted "set d -c off; rows 0; vserver locks nfsv4 show -inst" | tee locks.txt | grep -i "client name" | sort | uniq -c |sort -n