This is being investigated.
2.12 has the needed save state features so the cause is still unclear.
If the problem cannot be solved in a reasonable time-frame, we may need to revert to 2.11 turret features and suggest completing any needed additions via local changes to your mission (... pretty unlikely, as we are highly motivated to retain the 2.12 turret improvements).
However this gets resolved, it is the last blocker issue for 2.12 to leave beta phase.