Unity hangs after OnApplicationQuit, how to debug?

Hi community!

My scene seems to hang every time I try to shut it down. Happens in both the editor and a standalone build. When clicking the X button to quit the standalone build, Unity will apparently successfully call all the OnApplicationQuit methods (as evidenced by breakpoints, not sure how conclusive that is) but won't go any further - the scene is still there, stuck. Windows reports it as "Not Responding", CPU usage goes down to 0% in the Task Manager and a few threads seem stuck in waiting state as evidenced by Process Explorer. If Visual Studio is attached, pressing pause to halt the execution just leaves VS hanging there until the process is killed.

My question is, how would I start debugging this situation? VS doesn't seem to work and apart from probing at threads in Process Explorer I can't really figure out a way to do it.

Thanks for all your answers