@ColdIronPoz, thanks a lot for the call stack!
The logic behind the suspicious line is quite simple:
Step 1. rename old actor to something unique
Step 2. rename new actor to old actor's name
The only reason that Step 2 is failed (which causing the crash) is that Step 1 failed silently somehow. My theory is that unique name generator is not reliable during LoadMap call back. (Need more code digging to prove that theory)
My current solution is adding rename test before the actual rename operation to capture possible rename failure in the first place. Will be in next update.