First this was only with the new UI, now I also have it with the old one. I load up the game (either in the old or new UI), and it starts up, but before it shows anything in the headset, it crashes to desktop, or in the old UI's case, to the launcher. Two trace logs, first one was with HMD+mirror, the latest one without mirror.
It was this controller.json in the player folder that seemed to be the problem. I tried to edit it yesterday for the freelook camera. Didn't work. The game worked good after it though.