If I thought that cars were flashing me, I’d check all of my car lights, to be on the safe side. It is worth doing every so often, just in case. I check all of your lights and light combinations with a friend stood behind your parked car where they can see all of the lights to check if there are any electrical faults, lights that are not working or lights that are working infrequently. Also check the inside of your car boot to see if there are any loose electrical wiring. Or possibly wiring that is being infrequently knocked by the contents of your boot(shopping/presents) that is in turn causing infrequent rear lighting. I would also check my car fuses, usually placed under and to the side of your steering wheel, to see if there are any loose/broken fuses that may cause infrequent/no lighting.
There is one other thing that I’d definitely check out though, having been nearly caught out myself. There is a T junction near me, that when cars are approaching me, whilst I am waiting. It definitely appears as though approaching cars are flashing me, in order to let me out. Very fortunately I realised just in time that it is due to a fault in the road surface!!!
They are definitely not flashing! That may well be the case for you too!
One final thought, especially as this time of year when everyone is so busy rushing around🙄😉. Are you driving slowly, and cars behind you are getting impatient? If so, I’d just pull over and let them pass. Just be careful though if you’re driving down a lonely quiet country though!
Personally, these days due to a personal incident, I drive all the time without fail, with all of my car doors locked.