Are you an Administrator user ?
Are you sure you have the "Autobrowse" feature checked in RSWho ?
Try doing a right-click and "Run as Administrator" for RSLinx Classic.
Try deleting the Harmony.HRC and Harmony.RSH files in the \RSCOMMON directory.
These are all random ideas; I've never seen the effect you are describing.
RA Knowledgebase has a few ideas, including this one:
https://rockwellautomation.custhelp.com/app/answers/detail/a_id/9032/related/1