My new build is on Postgres.
The DB errors we've seen in the logs don't always coincide with the client disconnects. Fantastic, huh?
I may have spoken too soon when I said "Spark is still disconnecting" in this scenario - I saw disconnects right off but it seems to have settled down now. I'll continue to work on this and report back.
I really want to thank both of you who have taken the time to contribute to this discussion. I'm grateful.