Thanks for the replies..
murphyS90D - That's sound like a reasonable explanation but I haven't experienced this at a dealership where there are cars charging and cars next to them locked and not charging..... if this was the case dealers would get this issue all the time, and potentially charging location too..... so it makes this a bit more interesting...
JohnnyG - Great questions, this has happened twice in the morning at 5:00am so I didn't get the opportunity to experiment, but it does feel like it's when I unplug the car, as I opened the boot first on one occasion and unlocked the ca first..... I will experiment a bit more at a reasonable time. This happens only when I unplug the car, plugging in I've never experienced it.
If this was common I would expect places like the Tesla dealer as Heathrow to have found this issue.... I need to find the answer/solution as the alarm going off 5:00am isn't a great thing