Craftsman garage door opener 200.57933 - stuck half open, trolley is half way

Hello,

This is a replacement motor. The trolley is stuck about half way between the door and the motor. When pressing the remote, the trolley moves about 3 ft towards the door (closing), then goes back to where it was, and the light flashes...a lot, more than 20 times.
Any idea what's going on and how to fix it? Couldn't find this behavior in the troubleshooting section. It's not overheat for sure, we just plugged it in.
Also, when handling the chain or the trolley by hand, the light flickers (not sure how it is related to the light and why would it flicker as if there is a loose wire that is connectong the chain to the light.

Thanks.