I am currently making my forests destructible by identifying which instances are hit, removing them and spawning a new actor using the same mesh at that location. When that actor is destroyed the whole forest disappears and reappears then all the trees use the same LOD and the same orientation and …

I just fixed the SpeedTree flickering bug for version 4.11. It should be in Preview 2 which is scheduled for next week so it would be great if you could check it then.