I had exactly the same problem of my SmartThings Hub v2 not able to find my Hue Bridge anymore after I changed my router setup. I tried all solutions mentioned on the SmartThings support site but the Hue Bridge remained undiscoverable.
In my case, the steps below worked and allowed me to solve the problem without having to go through the dreaded procedure of deleting all my Hue devices and start over again. Hope it works for you as well.
- Go to http://graph.api.smartthings.com
- Select “My Devices”
- From the list of devices, select “Hue Bridge”
- Press the red “Delete” button
(to my surprise, I was able to delete it without warnings of it being connected to existing SmartApps etc) - Start your SmartThings app
- Click “My Home” and select “SmartApps”
- Click on "Hue (Connect) to start discovery of Hue devices (don’t forget to press the button on the Hue Bridge)
In my case, it found the Hue bridge instantly and I was able to easily restore my Hue setup.