This is the bathroom after having a re-seal/repair company try to fix the leak.

Thanks for your thoughts

We are on stumps and this movement is about as central in the house as it could be. There is quite a lot of drains around the house that we try to keep clear.

There is one medium sized and two smaller garden beds across the front of the house but these are at the other end- most near the bathrooms. We are on a slight slope with the front of the house uphill. Could these be the problem?

I don’t really want to take them out because they make the look of the house.

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There is one large gum tree about 10 metres away at the front (in front of the garden bed). all of the other trees and garden beds are away from the house.

The ventilation see to be clear but is there any way of checking?

If it smells musty it is damp

It smells a bit musty near the bathrooms but seems pretty dry down the other end near the cracking

The musty smell will be caused by mould spores in the soil. We had to get a couple of inches removed when we had mould remediation done. Smelled heaps better afterwards.
Sorry I can help. You need to try more experts like you have.

We had mould in our under floor area which we got fixed with a professional treatment as well as installing special underfloor extractor fans

sounds like you have highly reactive soils. We have them in our area... basically the ground is a peaty clay that swells when moist and contracts and cracks when dry. There can be a lot of movement, and basically concrete slab houses are not the ideal, and should be built with floating slabs. What you can do about it know though I'm not sure? It's a complicated issue and you probably need some expert help. I know there are moisture detection gizmos that could help shed light on what's going on. And have you check under your house to see what the stumps are doing? We're redoing our stumps and our builder plans to use adjustable tops. It means the house can move and if there is any significant drop we can easily adjust the levels. Also any work will be screwed rather than all rigid welding, we will avoid using concrete as much as possible, no slabs under the house so it can drain freely through a bed of gravel. I have found, not expert advice, just my observation that the ground moves less if I just keep it somewhat moist and spongy so it doesn't crack. I have also chosen water loving plants and I run the washing water out into the gardens, the downpipes now drain into a rain garden.
https://www.abewa.com.au/blog/article/12062017-455/reactive-soil-classification
A lot of people on the slopes seem to have issues, we rented a house around the corner and they seemed to think pouring concrete everywhere would stabilise things, but it seemed to have the effect of pulling the house down the hill. We're using plywood on the walls, as the original house had, as they can flex a bit and won't crack.

https://build.com.au/building-reactive-soil-sites
and this one has some great info....
https://buildingconnection.com.au/2018/03/20/reactive-soil-a-slab-of-confusion/

https://www.qbcc.qld.gov.au/sites/default/files/A Simple how to Guide to Preventing Structural Damange to your Home.pdf
This has some great practical advice and diagrams. I hope that gives you a useful starting point

https://www.qbcc.qld.gov.au/sites/default/files/A Simple how to Guide to Preventing Structural Damange to your Home.pdf
whoops I messed up the first link, maybe this will work

This was from that qbcc pdf I can't figure out how to link to properly.

now i know you have stumps but might explain the pattern of movement.

Thank you. That’s lots of very helpful information.

I am concerned that if we can’t stabilise the ground effectively- particularly under the bathrooms- that we are going to have ongoing cracking and therefore leaking problems.

it's likely whatever you do there will be some movement, its a case of minimising it. so choose materials that can flex, smaller tiles are less likely to crack a they can flex a bit, possibly the choice in grout too. i'm planning to clad my bathroom walls and ceiling in colorbond, but i love how low maintenance it is and avoids mould. timber always handles movement better. the reality is this should all have been addressed at the build/design stage and submitting plans to council but so often that seems to be overlooked.

our kitchen dining area was tiled, and its all cracking, but the bathroom is fine. i think it's just that the bathroom is smaller and the posts pretty much run around the wall so it all moves together, the kitchen/dining is just too big an area and the posts run right along the crack, so of course is really cracked and needs to be pulled off. lovely tile, but wrong choice for this house. i plan to use lino for the floor in the kitchen and bathroom, it would have originally been lino. our neighbour has a concrete slab under their house and i'd been puzzling how they stopped it cracking till they showed me they layed it in sections like massive pavers. this sort of soil is like big sponge, so i prefer to keep it moist and use plants that soak up any excess moisture. i've got water loving subtropicals, gingers and cannas and half the lawn is mint. look, don't panic, get to understand what this means and factor it in to any further choices.

are the stumps brick or steel or wood? you could look at replacing them under the affected area, run some extra drainage under there and use adjustable tops so any further movement can be adjusted. i like to think the soil dances.

replace with steel too! and screw everything so it moves, rather than rigid welding.