Android or iOS? I just checked and in my iPhone app the last speaker I used it with (Kitchen) is on top, not the alphabetically first speaker name (Bathroom).
iOS - iPhone 14 Pro or iPad Air. (Me). Spouse uses iPhone 16 pro.
Very annoying because we have to bring up all rooms (9 zones) and disconnect the room that's firing up in error.
It just occurred to me that the room that is becoming the incorrect default has its Sonos bar connected to the tv. I wonder if the tv (Samsung) or cable box (Xfinity) are booting up somehow, I'll investigate today.