Thanks, @hube2.
Some poorly commented out code seems to have been the culprit. It wasn’t throwing any debug statements, but I discovered when deactivating / activating the plugin, the WP dash would display a message about my plugin producing 72 “unexpected” characters. That was as precise as it got.
I would still *like* to know why I can’t seem to get my fields to be 100% functional across the network without using local JSON and manually synching at each subsite, but I can move forward for now.