I was fighting this for awhile before opening a case. It appears there is a defect where Agent Discovery of Linux agents doesn't work. This requires manually doing a List Resources on every single node.
While monitoring is still functional, the manual process needed is very costly. I just got done convincing the Unix team we can use the SolarWinds agents for monitoring their servers when I found this out. We have thousands of Linux servers on which I had intended to install the agents, which will take a significant amount of time to do now.
Is there an ETA on which release this would be fixed?
I'm hoping this can help get shed more light on this issue, and help anyone who may be encountering the same thing. If you have the issue, please open a case.