'Nail Pop' with screws? (Small Lumps in LVT)

Hi

I've fitted a floor with Karndean at the start of the year and a few raised circles have appeared over where I'm sure screw heads must be. I used floor-tite screws and all were feathered over.

I can't believe they're backing out but I guess it's possible? The only other thing I've noticed is they're on the same joist (metres apart), but can't really make sense of it.

Any advice really appreciated.

Cheers

 

Loose joist?

 

That was my first thought but it seemed okay and was 'noggined' to adjacent joists at either end (purely because I like to have the seems of the ply boards supported ,not because I was suspicious of the joists).

 

There's also no noticeable movement of the floor (neither creak or lifting feeling of boarding or bounce)

 

So there is definitely no play in that joist?
It sounds like it has something to does with movement

 

You answered before I posted, ignore my other post mate

 

You've lifted the plank then and how far out have they raised?

 

Nope, no movement now. I'm wondering if there was sudden movement and it's now settled? Clutching at straws really.

No haven't lifted the plank, was hoping for a few ideas before doing it, don't want to tighten them back down and them pop back up. From what I can feel/see it must be at least two or 3mm they've raised.
I might be able to get under the floor, not sure what they'll tell me but worth a look I guess