The G man.
I have the same issues on a few occasions of late when you expect to open the car on the cars buttons rather than using the remote - which works fine.
I have wondered whether some other signals are interfering but as it has only happened a few times not unduly worried.
What was strange on one occasion is that the "no key" orange light light came on when driving once but fortunately did not turn the car off Maybe the fob battery is getting low (nearly two years old, and if it means anything the car has done just on 10k miles) so I will get it checked at the next service later in September.