Hello, I believe I am able to help solve this problem for you, the steering wheel buttons on the left and right side of the steering wheel are connected to each other by a ribbon wire type of deal "Wire that looks like a ribbon" and what I would suggest doing first is carefully remove the airbag from steering wheel to get access to the steering wheel buttons, first disconnect 12v battery and secure ground wire off to the side, then there is a video on YouTube that shows a trick to taking off the steering wheel airbag called "BMW F30 Airbag Removal-Different way" posted by Rokan81, he makes that process a breeze just be careful anytime you are doing work on trim the plastic is not the strongest. Then once the airbag has been removed (Don't forget the screws on the back of the steering wheel they bolt into the steering wheel buttons which hold them in place) you should now have access to the steering wheel buttons.
Note how all the wires are routed and placed before removing anything, it is crucial that everything is put back in the same spot so that no wires get pinched or damaged, if necessary, take pictures and also if you set the airbag down, please make sure you set it down face side up (BMW Logo pointed to the ceiling). At this point just gently pull the steering wheel buttons out of the steering wheel, the left and right side buttons come out together as one assembly connected to each other by the wires. Now, remove the plastic housings on both sides of the steering wheel buttons held on by either 3 or 4 small silver torx screws (Can't recall if it was 3 or 4) and now check that the connectors are all connected properly, give them a slight push in to make sure there isn't a loose connection or if necessary, remove and reconnect the connectors. Also be sure to check for any damage to connectors or wiring and check for any signs of corrosion while you are already in there, reinstallation is just in the reverse order. Once everything is back together, reconnect 12v battery, clear codes if you can, then test drive and function test the steering wheel buttons and cruise control to verify they operate as designed and warning message no longer appears. When the cruise control malfunction pops up, the steering wheel buttons will not be lit up and also won't work during the duration of the message being on and will work again once message goes away before fixing the issue so the purpose of the test drive would be to verify that no longer happens. I hope this helps you, I had this exact same issue for several months and kept chasing my tail on this one and found ZERO helpful information and had to end up doing actual diagnosis to figure this one out, so I wanted to make sure I put a detailed response out there for someone having the same issue. Best of luck to you.
