The Philips Hue hub is discovered using mDNS on the local network.
Some debugging tips:
I guess you tried power cycle also the Philips Hue hub?
Try if the Hue hub can be found using our Android and iOS apps, without being connected to a Flic hub. That should help figure out if the problem is with the network connectivity on the Hue hub or the Flic hub.
You can for example use the app Service Browser https://play.google.com/store/apps/details?id=com.druk.servicebrowser to see if the Hue hub can be discovered on the network (look for _hue._tcp).