I had this thread and one other saved when my 2014 had the same issue. It was worse in the heat and would sometimes not even go all the way up. Never got to fixing anything before I switched to a 2018.
Here's the other thread on it with some additional detail:
https://f30.bimmerpost.com/forums/sh....php?t=1729917
https://www.newtis.info/tisv2/a/en/f...cks/1VnXHHnyP1