TomCat69 Hey, sorry it didn't work for you.
I've never encountered this issue but try doing this:
1. Make sure you are running latest OS
2. Make sure screen resolution didn't go to not the highest again
3. Check that phone is connected with cardboard properly (there might be issues if you run daydream on same phone)
4. Make sure Cardboard app installed from store
If nothing helps, try snapping a screenshot and posting it here. Also I'd need your OS version and we might need log files later.
Thanks, please keep me updated if this works or not
Best,
SLR