I did a few more scans, and played with moving plugs around. I have ~ 300 plugins in my vst folder, so scans take a fairly significant amount of time.
This is what I found:
1.) DX7 V causes Pluginscan to crash - I get a dialog box saying "pluinscan quit unexpectedly". Subsequently, DX7 V is listed as "Failed Validation".
2.) Pluginscan was hanging indefinitely on Farfisa-V. On one scan I waited 10 minutes, another scan for 16 minutes; afterwards hitting the skip button (which listed the plugin as "Failed Validation").
3.) Jup-8 V3 causes Pluginscan to crash - I get a dialog box saying "pluinscan quit unexpectedly" (the stack traces seem to indicate vsl code running).
4.) When I remove all 3 of those vst plugs, no other failures were reported (including no failures for Synclaviar, Vox, Wurli).
5.) For AUs, some of the same plugs (as the VSTs) fail (ie. DX7 V AU failed). Other different ones failed (eg. Mini V3).
6.) For all the VSTs that failed, when I removed them from the VST folder, did a complete rescan, put the vst plugs back, then did a 'rescan for changes' - those plugins did scan successfully, and did instantiate in VEP,
Again, my configuration is a MacPro (Late 2013, gobs of mem and disk), running High Sierra (10.13.6)
Hope this helps,
Kevin L