Agree look yourself first, someone here before had a good list of where
mould can come from....
New build enough, we had mould in corner of walk in wardrobe, hidden behind a huge xmas tree box....simple look outside a lump of cement under the tiles had come away and so rain simply blew into soffits and down wall cavity. Simple diy job to fix n dry out, kill n paint. Caused by powerwasher....
we lived years ago in apartment with no window in a tiny bathroom n we opps disconnected the fan as huge cold issue...we had asked landlord numerous times about a cover for it as missing but no, so stuffed it up...mould visible quickly where tiles meet the ceiling....