Have you tried re-calibrating the hi-hat and checked that the selected trigger type is correct? Sometimes there may be a software glitch or bug that loses the current settings.
It's also possible that there is some physical issue with the hi-hat pad or the controller. You could try plugging the hi-hat pad to another input or another pad to the hi-hat input and see if you can reproduce the problem.
It's also possible that there is some physical issue with the hi-hat pad or the controller. You could try plugging the hi-hat pad to another input or another pad to the hi-hat input and see if you can reproduce the problem.