I thought it could be that, and while I do like tight pants (TMI), it's not the case. Drove to work today with the key fob on the passenger seat and the issue recurred. Unlocking and then relocking without any driver input. Going over (speed) bumps or around corners seems to trigger it and...
Recently my 2015 i3 REX started unlocking and relocking by itself while driving. Seems to happen primarily during low speed cornering. Also, the right passenger rear door sensor will intermittently say the door is open (when it's not) also when cornering. The sensor will show the door closed...