You can try the double-luck voodoo trick:
If that fails, you can try to power off the hub (Setting -> Shutdown), wait for the red LED on the hub (shutdown complete), remove the USB power cable, wait 30 seconds, re-insert the USB cable and wait until the hub starts up (green LED). This will reset the Zigbee circuit/board inside the hub, maybe it got stuck in a weird state.
Also keep in mind that all IKEA battery-powered devices need to be paired really close (~5cm) to the hub, otherwise they will complete the pairing, but immediately fall off the network (buttons won't work).
Hope this helps!
