I had the same problem. I uninstalled Roon Remote, use CCleaner to make sure there are no remaining stray files, rebooted the PC, then reinstalled Roon again. Same problem! Roon Remote running fine in Android so I know the problem is not the core.
After a while the firewall pop up from nowhere requesting for access. I click to allow Private access and it runs great after that. This sluggishness has something to do with the firewall.
Edit 1:
I turned off the firewall and antivirus and it is still very slow. I see other threads also with Windows 10 having the same problem. Need @support for help.
Edit 2:
Uninstalled Roon again, use CCleaner, rebooted and installed the 32 bit version of Roon this time. So far, everything is flawless. I am using 64 bit Windows 10 and I am having problems on the 64 bit Roon version.