Hello,
Sorry for being quite late, do you stil have the same problem?
From what I see this may be either a slack timing belt or a weak stepper motor. I would suggest to tighten the Y-axis belt if you can, then try increasing the current intensity in the Y-axis stepper motor (by gradually turning the Y-axis potentiometer, the second blue box from the right. This should also increase the noise level of the printing).
Lionel