None of my Waves plugins were showing after validation, in addition to several other workhorse plugins. This was scary, but it worked for me:
1. Delete these:
~/Library/Preferences/com.apple.audio.AUHostingService.x86-64.plist ~/Library/Preferences/com.apple.audio.InfoHelper ~/Library/Caches/AudioUnitCache ~/Library/Caches/com.apple.audio.AUHostingService.x86-64 ~/Library/Caches/com.apple.audio.InfoHelper
2. Restart Logic
Everything is currently appearing and will hopefully stay that way...