My Z changes on my workhorse with every print. Sometimes even changing during printing. Any idea of what could cause this?
Gunk on the nozzle. Even .01mm of plastic on the nozzle can prevent a good electrical connection to the washer, throwing the measurement off by a random amount. The other three corners are usually pretty close, but the averaged out measurement of the wrong measurement can sorta be compensated for at the exact center of the bed, but the further you get from the center, the further off.