Just thought I'd straighten a few things out.
The errors messages I was getting on the console of the one client ("NFS: Server xxx.xxx.xxx.xxx error: fileid changed") appeared to be when accessing via NFSv4 only. I switched the client to v3 for 24 hours and didn't get those errors. I've just changed back to NFSv4 recently after changing my exports so the NFSv4 exports don't have the fsid=0 entry. Was reading that could cause the issue I was seeing and read that NFSv4 does not need the fsid= value. I can edit this post or comment later if I notice that I no longer receive the errors. Either way, I doubt any of this had to do with my issues with Kodi.
I no longer appear to be having issues with NFSv3 using Kodi. I'm not entirely sure if it was a CPU issue (which it could have been since at the time my processor was just about maxed out due to MergerFS and Crashplan hammering it) or if it was switching to no_subtree_check to the exports, or adding noforget to my MergerFS config. I have since moved to an entirely different motherboard and significantly more RAM and CPU power...simply because it fell in my lap.
All I can say is, after going to OMV4, things seem to take a little more tinkering and tweaking to iron out issues but I think this is all compounded with my configuration (mainly, MergerFS/Snapraid as there seems to be quite a few issues stemming from that in OMV4).
Confirmed, I'm not longer receiving the "NFS: Server xxx.xxx.xxx.xxx error: fileid changed" on my one client that was using NFSv4 after removing the fsid=0 entries in the exports file, and switching back to use NFSv4.