I've noticed this in many of the channels I subscribe to, 5 years ago they had something like 1m views on some videos regularly and now only 300k (or similar decline), all of them. Some of them even made videos about it. My guess, and theirs, is YouTube changed the algorithm and also the introduction of shorts.

Is the problem along the X Axis? Maybe you have X Axis Twist. Measure z offset on opposite ends of the bed along X. If they are different you need to enable X Axis Twist Compensation.