I copied the DLL files of a specific plugin into the VST folder that is configured for scanning in Reaper. All other plugins are found, displayed and can be used. This one doesn't. It's not listed in the "VST folders" view of the "Add FX" UI.
I have validated that the DLL files are actual VST plugins using the "VST Scanner" freeware. See the output of the tool with detailed report in attached file. Is there some incompatibility with Reaper according to the VST version or whatever? I'm using Reaper 4.78 64 bit.