In a Level Streaming setup, unloading a level that has spawned an AI Character with a Detour AI Controller causes a crash.
This was reported and tested in 4.23 (CL-8386587). This was reproduced in 4.22.3 (CL-7053642) and 4.24 (CL-9551884)
Results: Crash in UE4Editor_AIModule, UE4Editor_NavigationSystem
Expected: No Crash
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-81818 in the post.