A “hunting” valve is an operation of the valve where the on/off cycles are close together and so cycles the system too quickly. It is usually an off-design condition and wears out the motor or the other operator.
The problem of a hunting valve is not only the speed of the action, but also that the magnitude of the response is greater than required, so the valve “overshoots” the desired position and then has to return to a previous position, but again, it overshoots again.
so that instead of a damped oscillation, the “hunting” action is maintained or worse, the amplitude of the valve movement becomes greater. This is related to an unstable system, and the required tunning most probably need LESS gain.