force/torque sensor measuring unrealistically high values

[RaMathuZen]

Hi , I was recently working on tele-operating a UR5 robotic arm (virtually in PyBullet) using a haptic device. In order to provide force feedback, I added force/torque sensors at joint(fixed) connecting wrist_2 and wrist_3 links of the arm. When the arm's end effector is in free space the force measured along x,y and z was between 0.8 to 11 Newtons and when I make it to hit on a cube, it measures forces between 400 kilonewtons to 2 million newtons !. I don't why it measures such a high value ? and Why does it happen ? or is millinewton being used as a unit ?