I have upgraded to 11.2U3. There is one line that catches my attention in the changelog: https://www.ixsystems.com/blog/library/freenas-11-2-u3/
I'll give it another try with U3 tonight and report back.
Bug Separate ARC reclamation threads to prevent blocking disk I/O under heavy use
I'll give it another try with U3 tonight and report back.