How bad is this flooring

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We just bought this house and noticed this issue in the flooring, where each numbered tile:
1: worst bending, but the adjacent tile to the wall also moves with it (the 2nd picture is this floor)
2: solid as a rock
3-6: some level of bending but decreasing from 3 to 6

When I say bending, I mean compared to the adjacent tiles, and only each one of those tiles. What could possibly be the reason? Is it rotten floor joist or uneven subfloor? If there's issue, can a fix be done locally (i.e opening a part of the floor and then replace the floor) or do we need to rip the whole floor apart?

You might be able to get a survey or builder to look underneath with an endoscope to give you an idea what's going on, although the survey itself might be expensive and won't necessarily show exactly whats going on. If it's a modernish house it might just be thin joists or joists that have moved a bit. I had that and they just needed propping up on little brick pedestals. It might even just be sagging floorboards which have been cut by tradesmen for access and so are unsupported. Even if itsomething worse, it will be fixable.

@AudiobookListener thanks for the response!

We did get an L3 survey before, and the surveyor flagged the bouncy floor as potential timber decay and caused rising damp. We dismissed this as the claim about rising damp looked dodgy at best (it being a party wall, no visible sign or smell, and him referring his damp specialist buddy)

I'm about to dismantle the skirting board and scotia as those need fixing / replacing anyway. If while doing this, I remove several tiles to see underneath, will I be able to pop the tiles all back in after?

I had this on a btl property I bought last year. I knew there was a problem prior to the purchase. I got it a little cheaper. DH and DS took up the laminate flooring. Then took up floorboards. Took out rotten joist. Got a new joist and replaced. Then replaced floorboards including throwing 3 panels away. Then replaced laminate. It took about 2-3 full days but now it's as solid as a rock. The job will take at least 2 people to get the joist out. You will need to cement the new joist back in.

The damp can't be seen but if the joist is rotten it will likely have been caused by damp.

The cause of the damp could be one of a number of issues, though. Either way, it needs unearthing and sorting out. If it's just a joist or two, it's not a massive job. We replaced most of the joints in half a room here ourselves. But the cause of the rot needs sorting. Our predecessors failed to sort out the cause, and their remedial work 'sistering' the joists just meant the sistered ones had rotted in exactly the same way, at the same end. We took the lot out, sorted the cause out, and replaced the joists with DPC where they rested, and some new joist brackets, etc..

@caringcarer @BlueMongoose Thanks everyone for the response! How certain are you that this is a damp issue and that the floor joists are bad? I'm thinking of ripping off the wallpaper nearby, as the surveyor said the rising damp is on that wall. Will this be a good first step, or I will still need to open up the floor anyway?

With regards to replacing joists, did you end up having to dismantle all the floors and lay them back again? I have seen some quotes and they are very expensive. So I was hoping to avoid relaying the whole floor if it comes to that

You have to pull the floor up to see what the problem is. Floors cannot be fixed from above the flooring. Even replacing one floor joist will involve removing most of the flooring, depending on what’s beneath those tiles. So usually it’s not a ‘local fix’ but you are pulling the whole thing up.
Replacing joists is a relatively simple job, certainly within the realms of DIY.

I'd leave the wallpaper for now and focus on the floor. DH &DS did the joist themselves.its not a difficult job.

Sorry to jump on here, but I just came on Mumsnet to ask about a very similar problem!

OP - What are you planning on doing?

Everyone else - do you know how urgent this is to fix? Is it likely to cause more problems if I don't investigate/fix? If not urgent, I'd prefer to do work in another room first and sort this in around 3 months.

It can wait.

We recently put a new floor in our kitchen and had planned to have interlocking laminate tiles. The floor guy said not to as our floor was too uneven and to put vinyl tiles down instead as they are more forgiving. He said they spend a lot of time fixing the first type of flooring as even a few millimetres unevenness in the underlying floor can cause the tiles to pop up. Maybe get a flooring expert to take a look in case that’s all it is.

@Autumnleaves27 sorry to hear that! First thing that I did was stop panicking (felt really bad for my wife). For now we'll just focus on moving first, we're a bit slow in packing with a baby and toddler.

Once we move, we'll somewhat isolate the area and not put too many things there (difficult as it's living space, but we'll manage). Then I'll rip out wallpaper and skirting to check if the surveyor was right, we need to do this anyway if the joist is rotten to find the source of the damp. then open up the floor to see if the joists are indeed bad, which is quite likely now that I think about it. Then fix what needs fixing.

If the wall turns out to be damp, then we'll probably call damp specialist to get an opinion.

@HeddaGarbled ah fair point. I suppose if turns out there's no damp on the wall, we can probably call floor specialist first to assess before opening up the floor