Very strange, wonder if it has to do with the name of your first tab. Please rename your first tab to "TEST" instead of "1+1=3" and see if issue persists. That shouldn't be happening because the object is the tab object and not a blank object. If issue persists after trying the renaming please try disabling tabs within CB > Tab Management that could nest 1 by 1 until it goes away.

Please try disabling tabs within CB > Tab Management 1 by 1 until it goes away. This should tell us what tab is causing problems.

Ensure you're not disabling the core content tab. Core fields like user parameters for GID usage are present on it and if it's missing then it'll break some things. If you need to condition it I suggest moving fields to a separate tab and conditioning the new tab to avoid core fields from breaking. Aside from that I've no idea what's doing this as would need backend login credentials to review configuration.