Editor Crash when unloading level

So I have 3 scenes which I’m using as levels. The first scene contains nothing but an empty character, in order to allow the game to launch from a blank state. The second scene is a main menu with its own empty character. When clicking on the menu, the game loads a UMG widget containing a simple animated loading graphic. This widget then unloads the menu, and loads the third section (using Load Stream Level and Unload Stream Level), which is the game. This section has a custom player pawn inside the scene, which does not use a “player start” object.

The game itself has a pause menu, which has an option to return to the menu. On clicking this, what should happen is another UMG loading screen should appear, which should then unload the level and load the menu again. It appears to be doing this, but with one problem. When unloading the level, the editor (not just the game) crashes. It works fine if I just load the menu (aside from the fact that the menu appears on top of the existing level), but when I unload the level it crashes, and doesn’t produce an error message. I tried loading the menu before unloading the level, but that didn’t help. I tried unpausing the game, removing all other widgets, removing all instances meshes (as I heard terrain sometimes caused this issue, and since I don’t have any terrain that seemed like something that could be related), and removing the player pawn. All of these resulted in the same crash.

I really need to fix this, and soon, but because there is no error message (and nothing useful I can find in the logs), I have no idea where to start looking for the source of the problem. Obviously there is something in the third scene that is problematic (as the second scene loads and unloads just fine), but I don’t know how I can find it.

More information: If I use Open Level instead of level streaming, everything works correctly. It seems that it’s only the streaming systems that cause the problem. I hope, eventually, to create a modular open world, so hopefully this problem can be resolved before then.