I can confirm the following:
#1 Launch new install of Doric 3 and all VST paths are reset to the following:
At this point the Vst2xPlugin Blacklist VSTAudioEngine3.xml contains no entries.
#2 Next, I add the path for Kontakt:
#3 Finally, I click “OK” and Dorico freezes for a moment.
I discovered while it was “frozen” it was actually detecting Kontakt.dll from the path I added, and then putting it on the blacklist instead of the whitelist.
This happens even when I manually move the entries from the blacklist to the whitelist and restart–they are reverted to the blacklist and Kontakt is unavailable.