I cannot duplicate your issue, but I have a theory. If your remote is in close proximity to a smartphone (probably any, but in my case an iPhone), the signal from the iPhone screws up/shuts down the signal from the remote. Very easy to duplicate and a search of this forum and any other BMW forum will produce multiple threads addressing/verifying the issue. I have to make sure to keep my iPhone and remote in separate pockets otherwise I can't unlock/lock or start the car. If you have your phone and remote in purse, this could create a scenario like you are experiencing.