This problem generally means there is something wrong with the MOST bus, here are the possibilities:
1) One of the unit on most bus is dead/non responsive
a) Check BT unit, its most connection, its power connection, its fuse.
b) Check L7 unit for the same as above
c) Check CDC unit for the same as above
d) Check HUD for E6x for the same as above
e) Check any other fibre optic connected device like TV,DVD changer etc for the same as above
2) Open most bus connection
If MOST port is left opened, e.g. the port for OPS (in the glovebox) somehow become loose and its connector came off, very rare but possible.
3) Broken/twisted most bus fibre optic wire
Super rare but possible, if problem appeared after recent change/retrofit then look for twisted/damaged fibre optic wire
Problem will be among these possible situation. Generally I have seen if power is disturbed to a most unit then it simply breaks the most ring and you get this problem. To isolate it you need to buy most bypass part from dealer and you can individually bypass each component to see if problem is due to that unit. Isolate and identify is the key to work on ring topology network.
535d LCI, Xenon Adaptive Headlights, ACC 2 (Stop and Go), Lane Departure Warning
Retrofits M5 heated/lumbar/memory and active backrest adjustment seats, rear heated and folding g seats, SAT Shifter, paddles (SA2TB), HUD, Rear blinds, Electric steering column, SA430 Folding and EC Mirrors, High Beam Assist, CIC, COMBOX Telematics, DVB-T TV, JBL MS-8, JL HD900/5 + HD600/4, Morel HO II, Morel Integra XO, JL 12W6v2 and Jehnert in Audio.