Advancing / Rewinding / Film Error

I just got my hands on a green label contax g1 from a reliable seller on ebay and have run into an issue day one of having it.

After loading the camera I got about 18 exposures in and then the film counter bugged out and started flashing 00 as if the film was loaded improperly. I figured maybe it was user error since it was my first go at the camera.

With a new roll I got about 6 exposures before it auto rewinded mid roll.

I put the same roll back in and all seemed well then i got to shot 20 and the flashing 00 showed again.

I’d really like to fix my problem instead of going through the trouble of returning it

(The batteries are brand new)

Does anyone know what may be going on?