Hey Steve,
Thanks for the speedy response! Luckily, I was able to solve this and my headset is working perfectly again. I'll answer the questions, just in case it's useful to you guys or anyone else.
I'm using Cosmos.
I haven't changed anything in my room, but it was the first time I did the room setup in the evening, so maybe the change in lighting caused some problems. I have a glass door, but it's not causing issues during the day.
Somehow, the setup still didn't work when I tried it in daylight, but I ended up just deleting all files created for the headset (literally everything I found, not just stuff that the uninstaller removed), and after that I got the "slow" room setup again, which worked.
Very happy to be playing again!
-wanda