I'm having the same issues with my new rear LED lights, where in only one half of the brake light LEDs are illuminating.
In this picture you can see that the tail lights (three horizontal bars) and the left bank of LEDs are illuminated with the brakes depressed.
For comparions, these are my current lights with the complete bank of LEDs illuminated along with the tail lights.
With the new rear lights, you need to utilise the original bulb socket holders, which I picked up brand new from BMW this morning. The connections on the back of the new lights plug into the bulb sockets on the holder, with the holder then connected to the car. I checked both bulb socket holders with their original bulbs, to see if the issue was with the lights or with the bulb socket holders. In the picture above, the two bottom bulbs are the brake lights but only one of them seems to be working, which is the case on both holders. In both cases, it's the outside bulb socket. I tried swapping the connections around on the back of the light to the 'good' socket on the holder and can get both banks of LEDs to light up individually so that shows that there's no issue with the lights.
Looking closer at the socket holder and I noticed that there's only five pins in the connection with the bottom one missing. Interestingly, the missing pin runs to the non-working bulb socket.
Here's the connection to the car, again with only five of the six wires with nothing running to the "sixth" pin.
If I can get the 'false' socket working, I'm sure this will sort the problem but I've no idea where to even begin so any suggestions would be hugely welcome!