I'm facing a curious issue - I mount an NFS volume (ONTAP 9.4P5) to RHEL 7.6 or CENTOS 7 and if I leave it as it is and later (after 1h) try df -h it takes 1-2 minutes (and strace shows it hangs on the NFS volume). After that all commands targeting the NFS just work as they suppose to - $time "real 0m0.009s". When I leave it to "cool down" for an hour the problem reoccurs again.
There is no FW, storage is accessed on L2.
Workaround with df -h (or ll or whatever) running in the background periodically to keep the NFS "hot" is not an option.