Ain’t that the truth!

I had a customer using 18 month old red hat kernels (not patch for a long time)

They upgraded ontap to something modern and  either did not realize (likely) or forgot they were using nfs v4.1/pnfs. As soon as ontap finished the boot of the last node to the latest version, ALL the rhel boxes panicked. Upon review it was due to a bug fixed 15 months ago in the kernel. The fix was simple, Chang the mounts to v3. 

So sane thought, if you go down the 4.1 path it is best to keep everything current both client and server to avoid nasty bugs