OK HERE IS THE ANSWER.
And this might happen to almost anyone.
To see this problem you have to be signed into two iCloud accounts. Now you can do this. Some of us run a separate ICloud account as a Contact sharing mechanism for family or friends. You create a secondary iCloud account - it's OK with Apple - and then sign in on every MAC you want to have access - its strictly a contacts access - no mail, no calendar, no notes. Been using this for several years.
But it appears that Apple internally changed how this is treated when looking up a contact from mail in the contacts database. Having two or more sources for a contact information now confuses Mail and it can't look up the vCard for the contact - it can find the email address from entering the person's name, but if you ask it to open the contact it will give you a funny screen and won't be able to find it probably because it can't resolve multiple entries for one contact. As soon as I reduce the contacts database down to one iCloud account it started working fine for my 2,700 contacts.
And of course Family Sharing does not share Contacts.
So what to do?
Well it appears that for me, the solution is to stick with one iCloud account. I cannot share contacts with my family by using a 2nd iCloud account.
But I can sign their computers into my iCloud account and set it up as a secondary for them - they actually get access to my contacts and theirs and when they enter a contact which is very rare, I see it in my contacts. Their Macs no longer have the ability to previous a contact from Mail. Same problem for them. But at least we have somewhat of a family contact database.
I suppose the reason I didn't bet much help on this was that few if anyone uses Contacts this way. If you have a bunch of iPads, phones, and Macs all setup on the same iCloud account, well then that will work fine - only uses the one iCloud account. But if you wish to create a shared contacts database, then that's when you'll be looking for a solution that really doesn't exist from Apple.
What about Calendar? It appears that we share our calendars via iCloud - we share our family calendar and they subscribe - too bad we couldn't subscribe to a family contact list?
