On both the HoloLens 1 and 2, with Unity at least from 2019.x LTS through 2020.x LTS, with at least 2D windows/fullscreen and 3D immersive apps, with any XR plugin (or no XR at all), run-in-background enabled or not, when I exit an application by calling Application.Quit(), there's always a floating window left hanging out on the HoloLens.
Sometimes the window is blank, sometimes it contains a dimmed copy of the last rendered frame of the app, sometimes it's white with a big gray X'ed box on it, but it's always there. Sometimes the HoloLens cursor changes to the sleep icon over the window, and sometimes it doesn't. Clicking inside the window will relaunch the app.
I can close the window with the title bar close button, and it's not a show-stopper, really, but it's kind of annoying. On mobile and desktop devices, as well as other headsets e.g. the MagicLeap, the apps exit completely. It's a uniquely HoloLens issue.
There's nothing that indicates that the applications are crashing on exit. The VS debugger doesn't report any issues, nor do any of the built-in crash logs. Also, the task list shows the processes do indeed stop (their corresponding RuntimeBroker processes do keep running but AFAIK this is normal behavior), except occasionally certain resources seem to not clean up fully (but I am not entirely sure of details; I suspect it's related to video camera usage) until I close all the floating windows.
Is there any way to make the window close when the application exits? Is Application.Quit() alone not the correct way to quit on the HoloLens?
These windows, for example (video):
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