Mouldy bathroom floor

Is the plumber the same one who fitted the bath? If so, I would employ a new plumber to see if they can find the problem.
Just a thought but if it’s an over the bath shower, could water be coming over the side when using the shower?
As others have advised, I would take up the cushion floor and start from there. It won’t be too much to replace if only a small bathroom. Cheaper than changing the bath for a shower anyway.

If there are definitely no leaks the mould is probably due to moisture trapped in the vinyl flooring. Is the floor level? Moisture in a bathroom can find its way on a colder surface and if not dried out will eventually cause mould. Assume the room is kept well ventilated and warm?

Both---shower and a bath. Shower in the morning, bath at night.

Oh and just as an aside, we use a karcher to dry the walls and glass after every shower, just to try and offset any water seepage (what a horrid word) ?

I reiterate taking your cushion floor up, to see what's going on underneath, cleaning any mould and keep the window open to ventilate
Also I would contact whoever installed your bath and request that they kindly investigate the leaks
We removed our bath several years ago and replaced it with a large walk in shower and never regretted it

We had our bath taken a out and a shower installed. Some how water gets under the lino (inc splashes that run down the skirting) and the mould has come through the Lino in several places. Only thing to do is replace it.

Don’t think lack of a bath is very significant these days. We bought our house 27 years ago and it was notorious in the road as “the house without a Bath”. We had one put in but it was seldom used and tbh wish we hadn’t bothered. Were quoted £12k to replace Bath with walk through shower! Have different priorities ?

On a different tack.

We are going to update our bathroom. Will remove the bath, never use it, and have a walk-in shower.

Not bothered about re-sale value. We hope to stay here until we die, and shower will be far more user friendly than a bath.

Just a thought Stoker48, if the black marks are not coming from the bath leaks; have you cleaned your cushion-flooring, with a steam mop?
My friend did this and black marks appeared through her flooring.

Take up the cushion flooring straight away and see what is underneath mold only comes with damp and warmth so somewhere you have to get to the bottom of it Mould spores are dangerous you can kill them with bleach but always must find out the cause.get cracking today take up that cushion flooring asap

How odd. No never had this problem. I'd get in touch with the original installer of the bath. After only 2 years surely it should still be under guarantee?

Can’t see that a bit of mould is enough of a reason to get rid of a bath but then I hate showers! I’d just get your plumber to fix the leak. If you’ve got an over -bath shower, you have the best of both worlds. Taking the bath out would also reduce your pool of potential buyers.