QGroundControl enters flying mode when drone is armed (and landed)

I uploaded the latetest release and done all the calibrations but when I arm the drone QGroundControl detects it’s flying even though it’s landed (preventing also the disarming). In addition, I have the impression that rotors spin slower than usually.
The problem is certainly not related to hardware, might it be a wrong parameter? Someone has got the same problem and fixed it?
Thanks in advance for help