Did you restart the computer 
- Tried Powercycle that Light bulb?
- Reset the Bulb and Re-pair it (One by one)
See : Fixing disconnected Zigbee devices (without having to modify all flows)
If Homey says it is Paired already, Restart the IKEA Zigbee app!
This works for me most of the time with Sensors!
Last Workaround,
3) if it is added as new Light, the Device IDs are in the URL on the Web Interface and use the script here:
[HOW-TO][Pro][Cloud] - Tool to FIX (advanced) flows after removing and re-adding devices
