Memory seat rhyme and reason

So while this never happened once in 90k miles of ownership of my 13 SEL, at least three times now in my 15 SEL, with about 3k miles, when I unlock the door, the seat will move to memory position 3, which is my oldest sons. It’s typically after the third or fourth unlocking of the day while running around to different places so it’s not “bmw” style where it is remembering the setting of who last locked the door with which remote. I can be out half the day, with the same key, and all of the sudden when I unlock it the car will choose memory 3. Is there witchery afoot? Do I need a priest? Or can someone explain the way that system is supposed to work? Other than this strange issue, the car is flawless other than the leather on the drivers seat already starting to wrinkle and crease.

Memory seat rhyme and reason