Temporary maps issues like that are usually related to connectivity blips. You can reliably reproduce the behaviour if you spend any amount of time with the car in a known area that is out of mobile data contact i.e. If the area of no data is big enough you eventually lose the map refresh. Loss of connectivity can be one of (or a mix of) the following: car location in relation to data mast, temporary fault at data mast, SIM issue, car comms hardware issue, car mirror hardware issue, car software issue... take your pick!