Has anyone experienced a mushroom locking cam 'dropping' so it strikes the window frame when closing?

It has dropped by around 0.5mm to 1mm. As it is the bottom of a standard top hung window, on the second story, I am not keen to remove the hardware just to poke around. 

The cam is designed to be turned by an Allen key, with a 1/4 turn giving a +/- 1mm adjustment to the sash closing pressure. The cam on one side is 'firm' in the locking hardware, but the problem freely spins, and does not appear to be screw threaded so never tightens. I cannot see anything to suggest the hinge has dropped.

It is around 4 years old. I will approach the installer if no great ideas here.