Unable to find subnets from a seed router

So, I have run into the same issue. I have just today installed a demo license of UDT, and need to scan for ports. UDT uses Network Sonar to scan networks.

In Network Sonar, I successfully used a seed router to select subnets, and started that scan. I then tried to use a different seed router to create a new scan. NS now seems unable to find subnets. I have verified SNMP credentials and have used both RO and RW communities. I have tried with different core switches as the seed router (a Nexus, a 3850, a 4510, 1001x). I did notice that all the seed routers that failed were at a remote location. So, I tried a seed router at a location which has an APE to see if the seed router can work on a network local to the APE, nope. I tried another seed router local to the Orion primary poller; that worked fine (it was the mate of the original one I used). I then tried a different local seed router (a WAN router), no dice.

So, I thought, I would select another MLS as a seed router, of the same model as the first one I tried, a Nexus 7010. It worked!. So, I tried a Cat 6500; worked. Tested a Nexus 93180YC; worked. tested a Nexus 9504; worked. Tested a ISR 4431; did not work. Tested an ISR 3945; worked too. Tested a different 3850, no worky.

Any ideas why Network Sonar can use some devices as a seed router, but not Cisco routers/MLS of current models?

Having same issue with seed routers here on Juniper. 

Can't seem to find an official doc on what oid's network sonar discovery uses, but I did find the list that IPAM uses, i would hope they are similar.

Probably the best way to actually be sure would be to grab a wireshark capture and launch your discovery to see which ones they are looking for.