First make sure you a pressing the buttons hard enough. If this doesn't work, it may be that one of the buttons was pressed for a long time causing the Hue tap to disconnect from the Hue system. You can easily reconnect the Hue tap withthe system without losing your settings.
Go to the Philips Hue app Settings menu and select "Accessory setup". Tap on "+" and follow the onscreen instructions.
The Hue tap is re-connected again.
If not, please reach out to our customer support for help.