You can see that your grid is not leveled and tiles don't lay flat on it. Level the grid as needed by lowering and raising the wire as needed to have a perfectly leveled grid.

They have a suspended grid kit that has leveling clamps that you attach to the grig with a string and you stretch the string from one end to another or you can make your own using small clamps from a Box Store and clamp the sting to the grid.

This is the kit

Or hand-clamps with a string

Clamps a string to the track and pull it across the grid and as I mentioned before make nessesary adjustments by lowering or rasing the grid wire.