DIAGNOSIS The switch is communicating directly with the bulb via Zigbee (direct bulb control), which is slower and less reliable than routing the command through the bridge.
FIX Reconfigure the switch in the Hue app to use the bridge as the intermediary.
- In the Hue app, go to Settings > Accessories.
- Select your dimmer switch, then tap "Configure."
- For each button, under "Press," choose "Hue scene" or "Activate a Hue scene" and select a scene you've created, instead of the default "Control lights directly."
IF THAT DIDN'T WORK The switch's battery may be low. The Hue app doesn't report this. Replace the battery (CR2450 coin cell).
HEADS UP If you configure it to use scenes via the bridge, the switch will not work if your bridge loses power or internet, as it's no longer controlling the bulbs directly.