Assuming you’re referring to this app: [RELEASE] Humidity and Temperature Management with Scheduling (homes without HVAC/thermostats / using heaters and cooling appliances / vacation home / remote homes)
It has a separate setting for lower and upper humidity settings, make sure you’ve set the upper limit if you want the app to turn off the humidifier when it cross that threshold. Also note it will send a command to turn off the humidifier when the threshold is crossed (also account for the swing value that you’ve defined), which means if you’ve set it and it’s not turning off then either the sensor isn’t reporting the humidity or the switch isn’t receiving the off command.