So it turned out that for that specific repository there were some pre-hooks, located in:

/git/repositories/@hashed/74/86/784285826527........git/custom_hooks/pre-receive

This was the hooks path before version 15.10. It can be found from gitlab panel: Admin --> Overview --> Projects --> (your project) --> Relative Path

This hook was timing out for me and had to be re-configured.. I checked all other directories, except for the @hashed one .. ^^