Steps to repro:
1. Open attached project "case_1196582-2019.3.0b10_Repro (1).zip"
2. Open "Load Scene" Scene and enter play mode
3. Press on "Load Scene", wait for around 30 seconds and then exit play mode

-observe the crash-

Reproduced on 2020.1.0a15

Note: Could be related to Case 1192129

First 4 lines of the stacktrace:
UnloadAssetBundle
PlayerLoopController::ExitPlayMode
layerLoopController::SetIsPlaying
Application::TickTimer