Most probably the plank is not tightly attached to the floor underneath and that's why the plank is moving up and down when you step on it. The subfloor might be uneven and that can't be fixed without dismantling the whole floor. The other option is that the floor doesn't have sufficient expansion gaps by the walls which causes the floor to raise up in the middle as the floor is not able to expend sideways. Now in the mid-September air is very humid and laminate is expanded compared to dry air conditions of winter and spring. If that's the case, you can remove the skirtings and check if the laminate is touching the walls. If it is, you can use a multi-tool to cut some laminate off to make the gaps bigger. That's should help.
What is the cause of laminatti wobbly in one place ?? , and how to fix
Most probably the plank is not tightly attached to the floor underneath and that's why the plank is moving up and down when you step on it. The subfloor might be uneven and that can't be fixed without dismantling the whole floor. The other option is that the floor doesn't have sufficient expansion gaps by the walls which causes the floor to raise up in the middle as the floor is not able to expend sideways. Now in the mid-September air is very humid and laminate is expanded compared to dry air conditions of winter and spring. If that's the case, you can remove the skirtings and check if the laminate is touching the walls. If it is, you can use a multi-tool to cut some laminate off to make the gaps bigger. That's should help.