Charge Flap will not stay shut!

[Raxacorico]

I charged my car at home last night. The vehicle was completely covered in frost this morning.
I've just been out to remove the charge cable but didn't notice an unlocking click (double click on the key).
The cable came out and I pushed the flap to the closed position.
I then wrapped up the charging cable. As I turned back to the car the flap was open again!
The pin that gets pushed in by the flap rotates OK to turn the catch, but the flap simply opens again, apparently not engaging.
Any ideas please (apart from sticky tape!)

[Raxacorico]

Finally got it to stay shut with gentle pushing. Locked the car, then unlocked it again, now the flap won't open! Grrrr

[Raxacorico]

Just been for a short drive. Came back, the flap now opens and closes normally!
I've charged overnight in the rain many times, but this is the first time with a frost; perhaps that was it.
Either way it's now working properly - we live and learn ...