Bronica ETRS film winding problem

Hello all!

Today I got my Bronica ETRS in the mail. The post office must have dropped it a couple of times because it was damaged when it got here.
When I put film in the film back, the first couple of shots work fine. I wind the film crank, it stops turning, and I press the release button. But sometimes it just doesn't work. When that happens I can keep turning the crank and nothing happens. Then suddenly it catches on again and it winds the film.

So to be clear. It feels like it cocks the shutter when I turn it. But it doesn't stop after that. It keeps turning and it doesn't cock the release button. After a long time it loads the release button. It's really really annoying. How can I fix this?

Best regards.

First I thought that there was a problem with the connection between the body and the film back but as I turn the lever, the filmspool on the back turns with it. It just doesn't advance..