How can I strengthen this squeaky new floor?

[JohnD]

 

[big-all]

save on the extra screws with a skip

 

[redhexagonal]

yes i must admit i thought it was 4 screws along a 1200 board so 45/400/800/1155 hence my comments off 6-9" for extra [7-8"] 50mm although wont do damage as such it will just be far more screws to remove if it still doesnt work to cure
i suspect the floor has jacked up in areas [screw pushes floor off the joists a bit before cutting in ]so removing screws loading up with a foot and screwing tight with extra glue will help but as we all know there can be several causes and possible solutions

They used spax screws so it shouldnt have jacked up? It does feel a bit like the board is coming slightly off the joist though, but equally it could be the joist is twisted a bit, they were in a bit of a state and had to be cemented into the wall properly