I posted on answerhub but figured I would see if anyone on the forums had some suggestions
If a destructible mesh has dynamic shadows enabled, after the mesh is destroyed and all the chunks are removed, the preshadow cache depths for each DM continues to to affect the scene render time.
In my test adding around 1.75 ms for each DM. Or 35ms total for 20 DMs
Since it never stops affecting the scene even if the actor and all chunks are removed, every time a mesh is destroyed, performance will drop and never get better.
The obvious immediate solution is of course to turn off dynamic shadows for destructibles. But is there any other solution?