Intermittent fuel flap lock issue

[jordanbutters]

So a little while ago my RS4 Avant's fuel flap lock stopped unlocking (but always locked). I thought it was a dodgy actuator so I've replaced it with a new OEM one from Audi, but when installing the new one I tested it and it didn't work either – same thing (always locks, wouldn't unlock). It was getting dark so I put it back on the car and lo and behold it starts working perfectly.

A few days go by and I test it now and then and it always works fine. until the first time I go to refuel and it refuses to unlock again. Exactly the same issue – always locks, doesn't unlock. It can't be the actuator and both old and new did it, and it doesn't seem like a signal fault as it'll lock every time without fail.

Any suggestions? It's such a small and annoying fault but one I really want to try and sort!