OP
I use the hair dryer to dry out some potential moisture. No sign of water in.You say that you have dried lights with a hair drier,
I would be amazed if this fault has nothing to do with water ingress.
The fact you have dried them suggests they were wet.
Also, could there be a junction box somewhere full of water?
Also no junction box. Straight from the switch to the holder. Each holder is connected to each other in parallel with the straight connectors, that I also changed with a brand new wago 221 ( I guess)