I have two UR4 receivers and have them and my computer connected to a router. I'm using Wireless Workbench v5.0.3. I am using DHCP and have verified the IP address and gone through the troubleshooting on the FAQ. The UR4 receivers do not show up in the Wireless Workbench software at all.
It's good that you have gone through the troubleshooting FAQ as those are the first things to check.
We have had some people with these symptoms that have a damaged router. Try connecting to a single receiver via USB or via an Ethernet cable without the router. If that works, then try a different router.
Also, note the lights on the front of the router to see if they are acting normally. If they are acting abnormally, the router might be damaged.