If it works slightly then maybe it’s not unplugged, but it could be just loose or a dirty contact to the strip maybe.
Keyboards I’ve opened have had normal multipin ribbons for the actual keyboard velocity switches, but then a simpler basic cable going to one end of the key action for the aftertouch strip that runs under all keys.
Something like this:
The strip hanging out with plug is for aftertouch. And in case you didn’t know, the two vertical white bars mid way along under the key are the velocity switches, a sensor under each. The short time difference between the first and the second being depressed is what is measured to create velocity. More advanced actions now sometimes have triple sensors, especially on digital pianos, to sense when the key leaves the top, for rapid re-triggering of notes.