Well, I shifted all the appliances off the floor 
rolled back the vinyl, and checked all the screws. Most were fully tight, a few moved a fraction of a turn, a few moved several turns although I had torqued them all down pretty tight with the drill to the same setting, and checked them with a screwdriver
I have not put the vinyl back (it is damaged now with going up and down so often) so I will walk about on it for another week or two and see if it goes loose again.
Some of the screws are now pulling into the countersinks quite a long way, so I will go up a size if I need to do it again.
rolled back the vinyl, and checked all the screws. Most were fully tight, a few moved a fraction of a turn, a few moved several turns although I had torqued them all down pretty tight with the drill to the same setting, and checked them with a screwdriver I have not put the vinyl back (it is damaged now with going up and down so often) so I will walk about on it for another week or two and see if it goes loose again.
Some of the screws are now pulling into the countersinks quite a long way, so I will go up a size if I need to do it again.
