I looked through a few support tickets where users have experienced that same issue that you have and restarting the Server(frontend and backend services) appeared to resolve the issue on multiple occasions.
Did you recently make a configuration change to your AppMon environment or upgrade the server? Those are the only things that I could think of that would cause the server to have issues processing your PurePaths.
We upgraded 7.0 in the beginning of August, but the other day we had an issue with our 6.3 collector service got turned back on. We had a few agents that recycled while the Collector was runnning 6.3.
Could this scenario have casued this? We can try to restart both services at night if that would resolved.
That service start up could have caused the confusion, what I think happened was the 6.3 collector service connected on the port you are using and though the service was stopped, the port was never freed. This is most likely what is causing your 6.1 collector to not connect to the server.