Try this:
1. Switch the optical boards for the X & Y and see if the problem follows the boards or if it stays with the Y-Axis.
a. If it swaps to the X, then it's a Happ optical board issue.
b. If it stays with the Y, then it might be a mouse controller problem.
If you can, next swap the X & Y connections on the mouse controller.
If the problem stays with the same axis, then you have a mouse controller problem.
If the problem switches axis, then you have an optical transceiver problem. (not the red board, but the IR transmitter/receiver)