HWD - For your information:
Hysteresis is a property of systems that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. For instance, if you push on a piece of putty it will assume a new shape, and when you remove your hand it will not return to its original shape, or at least not immediately and not entirely.
Didn't think that ALTs had any damping/ beyond the spring on the aneroid capsule and the capsule itself? Would be interesting to find out what happened.
My idea would be cr*p in the needle or subscale gearing or maybe even a loose needle?