You have a short circuit on the wires in the left side. It's a group of 5 wires coming from the PCB to the 3.5 mm connector. Those wires get smashed by the vibration and start to short or simple opens killing a channel. It is a though job, but you have to open the left side, top and bottom, loose the cables (glued and soldered) and try to isolate the wires making sure they aren't broken. It is a micro connector with 5 wires. The red one is the control that probably is shorting. blue and black are pos left and right and green and gold are the neg left and right.

Anyone knows the model of the connectors on the PCB’s?

I’m trying different JST connectors without success.