At first I thought this was just a fluke, but then it happened again.
In a formation of 3 bombers (B-17s in my case, not sure about other bombers), when the Lead bomber has a horizontal stabilizer torn off (right side in my case), the drones that are totally undamaged no longer maintain formation with turns. it's like they try but they have less than 5% of their normal turning ability.
I went ahead and bailed out of the bomber missing the horizontal stab, and when taking over the other aircraft, the remaining drone formed up immediately with no issues.