The transmission fault status shows when there is a problem that would effect the operation of the transmission. This can be caused by many things. The way to help figure out the root cause of the transmission failure will be to have the fault read out of the vehicle. I would recommend the dealer as more information can often be found on the fault occurring. However, a shop you trust is also an option if they have the BMW software to read out the faults.
Some items I have seen are problems with the mechatronic sleeve due to low fluid from a leak in the seal, pins coming unsecured in the connector to the mechatronic sleeve, PT-Can bus wiring issues, over voltage from a failing alternator causing the vehicle to enter failsafe mode. It will be important for the technician to look closely at the faults to determine the overall failure. Make sure they check the voltage at the time the fault sets, as I have seen alternators cause a problem like this. The dealer can see this information, but I do not think non BMW shops will be able to.
I hope this information is helpful. Please accept and best wishes on your repair. Thank you.