On the XTR 9000 / 9100's its all to do with the bleed. I swapped levers (from M9000 to M9100) based on some internet BS reports that the redesigned lever/master cylinder would cure the variable bit point. It did not. Then I took extra, extra care with the bleed and that fixed the issue. I should have known better than to take someone else's word for it.
BS internet no if it's on there it's gospel.
I think there are a lot of variable to this one. No 2 cases are the same.
My assumption was it was coming from the lever. ASSumptions can make an arse of yourself.
My theory was that once brakes got hot, the wandering bite point came back. I'd bled them many times with the same outcome. Worked fine till they got real hot then away again. A lever bleed always fixed this for a while and always got air out (quick flicks). This was m8000 and also a troublesome 9120. The 9120 was eventually fixed with new barb olive and connector. I've fitted 9100 levers to m8000 calipers, quick bleed and been faultless.
If I was to ride 70ks with say 300m elevation I wouldn't have a problem with wandering lever.
If I rode 25ks with 1300m elevation it was there.
My ASSumption when hot it was putting more pressure at the lever and air was getting in.
All my brakes with newer lever once bled properly have worked perfectly. More time spent doing a thorough lever bleed helps in my opinion.