FF suddenly doesn't connect to Firebase (CMS error, permission denied, Regenerate Config Files useless)

I'm having a big issue with a normal and working project, until 12 hours ago.
Suddenly FF stopped working with Firebase and started to show errors related to permissions, like when we want to edit Firebase data in the CMS:

I use a Pro plan integrated with GitHub. FF support doesn't know how to provide effective support.

The project was launched 2 weeks ago, we have some clients running only the Android app, and now I can't update the app! It's frustrating! We are small and every client and every update counts.