Two-Factor Authentication fail

Good Evening,

I have an issue with the Two-Factor Authentication. I used the Google Authenticator for 1 month and it worked pretty solid. The installation was easy and I had no problems. 1 week ago it stopped working. I tried to log in but the code was invalid. After 20 attempts with different codes, I used a recovery code. Now I disabled the Authentication, reinstalled Googles App and tried it again. The setup process is already a failure. I scanned the QR-Code, the app found it and displayed codes. But they don’t work. Even if I try to add the entry manually it doesn’t work.
I use GitLab on my computer and have a OnePlusX with Google Authenticator version 5.00.

I would appreciate your help!

Greetings, callypo