If it were just mould in the shower, it could be a question of some people (?men!) not understanding that showers are not self cleaning, just because water sloshes around when you wash?! (So do bacteria!)
I have a LTR with 2 ensuite bedrooms rented to 2 strangers who don't know each other. My male tenant keeps the shared downstairs clean & reasonably tidy, but has grumbled to me twice in 6 months that the shower gets mouldy! - I said he needed to clean it! And recommended a scrubbing brush & some bleach. My tenant seemed genuinely puzzled at this revelation! In contrast, my female tenant, who recently left, left her shower like new, not a speck of mould to be seen!
So shower cleaning lessons could be the answer, @Michelle1667 , as Lisa hinted?