Error enabling SAST

Installation: self-managed GitLab Omnibus
Version: 15.11.6

After multiple upgrades from 12.8.1 to 15.11.6, I am trying to enable SAST in a project but I get the same error all the time.

When I create a project I mark the option of enabling the SAST, but after creation in Security and Compliance > Security configuration I see that it is not enabled:

I try to configure it clicking in the button shown there “Configure with a merge request” but this message come up:

And a branch is created with this name “set-sast-config-1”. In this branch the README is modified with some basic GitLab info.

Do you know what is happening here?