There are three types of beeps. One is when press any button on the keypad (most keypads don’t beep for this but instead just light up to show activity on the buttons).
The most common beep is when it communicates successfully with the hub. So if you find the keypad lights up but there’s no action from SmartThings and the keypad doesn’t beep it means the mesh has an issue, i.e. the message isn’t reaching the hub or the hub response isn’t reaching the keypad.
With this keypad model, if the keypad “loses” it’s connectivity with the mesh, then you’ll find the top row 3 arming buttons start flashing serially. If they don’t flash serially but there’s no beep that means it’s connected to the mesh but somewhere along the route the packets are being lost (in either direction). If rebooting the hub resolves the issue it may point to an issue with the hub or some repeater close to the hub.
You could try to rebuild the zigbee mesh as explained here: FAQ: How to remove ghost devices from your z-wave and zigbee networks