We've seen that happen too. There is a persistent and very weird bug where an entire Access Level will suddenly go from it's normal settings to 'No Access' on absolutely everything. And then some time in the future, go back to behaving normally without any action from us.
If you want to confirm that it was/wasn't any of your changes specifically, go to Setup -> Audit Logs and filter on Log Type 'Access Levels'. That doesn't track every tiny change, but it would capture if you accidentally set something from Edit to No Access entirely.