Enable / ask your network folks to enable ICMP11 traffic to the poller (or other device) you have the probe on, see if that helps.
If its broke, I'd open a ticket. But in the spirit of giving you something to try, I'd install the agent on another device and try the path from it. It may be the agent on your server.
It was previously working so icmp traffic/routing should be fine.
It was only when IPAM was installed and then removed which it stopped, seems like it has broken something with the install maybe.
Could be the local agent not receiving the data correctly! worth a test as you mentined.
Have you tried to run Configuration Wizard? If not - I'd suggest to do it. If no result then run SolarWinds diagnostic tool (...Program Files (x86)\SolarWinds\Orion\SolarwindsDiagnostics.exe) - it will help to find out the cause before you call SW support
In latest version of NPM - the tool I ment is in another folder: ...Program Files (x86)\SolarWinds\Orion\ActiveDiagnostics\Solarwinds.Orion.ActiveDiagnostics.exe