This sounds familiar somehow :-) ... as mentioned quite some time ago, I have the same symptoms here, though - luckily - not too serious so I can live with it.
This is something even the mose careful calibration is unable to correct, and is caused by mechanical imperfections, usually towers not being spaced or angled perfectly. Alas this is hard to fix unless the design allows mechanical adjustments for those (and even if it did, it wouldn't be easy to measure it precisely with amateur means).
Ever wondered why Johann's autolevelling hard- and software doesn't go for dialing in the three tower home locations only (which you can to with careful manual calibration already), but probes (and then applies) a transformation matrix at many points all over the bed?
This is something even the mose careful calibration is unable to correct, and is caused by mechanical imperfections, usually towers not being spaced or angled perfectly. Alas this is hard to fix unless the design allows mechanical adjustments for those (and even if it did, it wouldn't be easy to measure it precisely with amateur means).
Ever wondered why Johann's autolevelling hard- and software doesn't go for dialing in the three tower home locations only (which you can to with careful manual calibration already), but probes (and then applies) a transformation matrix at many points all over the bed?