It’s an easy check, remove your x-axis and drive your y-motors. Both Y drives should drive smoothly & together. If one side doesn’t and you can hear the motor driving ( it may move with assistance) that’s your problem side. My left side drive was completely loose.
Follow the video, no need to remove the ball screw entirely, just need to remove it enough to access the coupling & retighten. I would suggest using Blue loctite on the coupling screws to prevent them from loosening off in the future. The ball screw nut should just touch the bearing, do not over tighten when reassembling.
From OneFinity “make sure the tension nut for the ball screw is JUST loose enough to let the washer move freely. Too tight and it won’t rotate.”