Thanks for the tips. I cut a bit of paint away, damp down the join. Not saturated thankfully.

Once it stops blowing a gale I’ll stick my head up into the roof and look for anything obvious.

Thanks u/--Ty-- and u/Guygan!

Every so often this bubbling gets worse. Today it is now about 50cm longer towards the ground but hasn’t moved for many months. However we got a bunch of rain and have high humidity today. It is in the toilet which is internal to the house, no walls shared external.

Is it a water leak in the roof? Poorly finished paint or plaster? Something else? The bubbling feels cool but isn’t wet and I cannot see water on the wall.

Australia. Home is about 10yr old.

https://imgur.com/a/Awt8aVN/