taflix's post in [6.10.3] Warning: Share xxx references non existent cache pool yyy was marked as the answer
Thanks, but I figured it out. I added SSD drives as cache pools. Upon initializing the drives, the default file system is XFS.
However, after poking about in the forums, reddit, and other sites... many suggested that BTRFS is better for SSD cache pools.
I changed the file system but didn't reformat the drives.
The common errors plugin could probably be tweaked to take into consideration this scenario.
I'll leave the solution here for future googlers to find.