When pressing the "Crash" Button in the attached (minimal) example "QtWebEngineProcess.exe" will stay open. If the program is closed regularly however, it closes correctly. The index.html keeps javascript busy by reconnecting a websocket on connection loss, which permanently occurs here because the host application does not start a websocketserver. The problem probably has nothing to do with WebSockets. Just illustrating the admittedly questionable code pattern. But IMHO whatever the state of the javascript execution can be, QtWebEngineProcess.exe should shut down orderly.

PS: index.html has to be put in the application runtime folder.