So I found this on the 5 series G30 forum and sounds like it's affecting many models with the Drive 7 system.
https://g30.bimmerpost.com/forums/sh....php?t=1802359
Someone on there changed their Bluetooth AVRCP version to 1.5 from 1.6 on Samsung/Android phone.
I made the change last night and today drove a good couple of hours throughout the day and didn't have one reboot using Bluetooth to my phone.
Typically it would reboot randomly between songs or in the middle of a song pretty consistently.
I don't know if iPhone has the same setting but if you have a Samgsung I would make the change on your phone.