I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.this can be caused by many things
the main computer that runs the system is one, water in the boot is one, but also any of the control modules in the system (Bluetooth, radio, etc) can also cause it and take the system offline, causing the symptoms you have
one thing you can try is unhooking the battery for an hour to preform a hard reset, but more than likely you have a failed module somewhere in the systemunfortunately specialized equipment is required to diagnose this system, and when components are replaced, they require special programming. there really isn't anything that can be done at home besides checking for water in the boot, per the system's design. You dont need a main dealer, but definitelly a BMW specialist with the equipment for this type of testing. Unfortuanately I cannot make a local recommendation.Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.
If it is a failed module, why would it start intermittently?