Try deleting the
HPDBookRemoteURL key (see Authoring Apple Help).
· on per-application basis:
defaults delete /Applications/MyApplication.app/Contents/Resources/MyApplication.help/Contents/Info.plist HPDBookRemoteURL
If you catch the outgoing connections with Little Snitch, the problem will be rather getting to know which application's help book is triggering it, as the URL might point to a cloud server whose name won't contain any of the author's data, see below.
· on a cache basis
cat ~/Library/Caches/com.apple.helpd/HelpCache.plist | grep -C 2 HPDBookRemoteURL
<string>/Applications/DEVONthink Pro.app/Contents/Resources/DEVONthink Pro Office.help</string>
Then you might want to clear these other caches
~/Library/Caches/com.apple.helpd/Cache* and restart