Agreed on thorough cleaning or replacement.
We have another discussion on the limitations of these switches/repeatability. Do you have accumulated chips on/around the bumpers or the switch?
Think of how it homes in terms of how that relates to your error.
The machine approaches the limit switch at a faster speed from whatever initial position it is at when called upon to reference to initially find the limit switch, then it approaches it again at a slower speed, as I would understand, the second run is for accuracy/repeatability and what it would actually use. The controller is able to time how long from where it was commanded to move from where it was moved to after the initial contact to the second contact.