If your battery and alternator is in good condition, this should resolve your problem. BMWs have a hard time when voltage drops to a certain level. I believe the Ignition or accessory wire was not receiving the correct voltage. BMW dealers are not the best in solving problems when they are intermittent or if no error codes are thrown. I have found these same problems you have described in several BMWs due to the build up of carbon or worn electrical contact in the ignition switch. This is a simple replacement and takes about 15 minutes and $75-$100 for the part. I have found the ignition switch would send out as low as 4-5 volts to the purple lead and several modules will fail such as the DSC, transmission, heated seats, steering wheel controls, airbags, and stuck brake lights. The tell tail sign will be no error codes thrown when this occurs. Good luck!!