I had this issue, it started to be intermittent and then just stayed permanently.
The fix was 2 separate visits to MG, the first to diagnose that it was a faulty TBOX. They only managed to troubleshoot as they had another ZS on the forecourt and that fixed it, but as they're hard coded to the car I couldn't keep it and had to go back.
What was disappointing was it took an initial visit for them to say wait and see, then the second to diagnose, and a third visit to actually fix. The upside however is that I had issues with the app to remote control my car, and this resolved it.
Whilst they were there they also updated the software. I still have a confirmed issue with using aircon controls whilst airplay is on, no fix for 6 months yet.