@ocdtrekkie I imagine some sockets without proper covers.
It didn't happen before, but it happened during the strong typhoon two weeks ago and the strong rain last week, and today only somewhat strong rain (50 mm/h) tripped it. Currently it won't come on again, I'll try again in a bit. I don't have access to the roof.
They dismantled something on the roof after the storm, a shed of some kind. That might have uncovered something that was previously protected.