Problem solved:
*Opened battery, read voltage directly (23.2), bypassing BMS, thus confirming that BMS had kicked in due low voltage
*Ran heavy duty test lead from internal Neg post to external Neg post, bypassing BMS
*Opened breaker to the array, closed battery breaker
*Charger woke up
*Closed breaker to array
*Charging began
*Disconnected Neg - Neg test lead
Post-event analysis:
I had set Bulk/Absorb too low (27v) and had a few very overcast days. Hooking up the lawnmower battery charger must have pulled the battery below the BMS cutoff point. The 34 volt reading is still unexplained, assuming it was spurious.