I have a large group in Contacts (~400) that I update monthly by deleting the group and importing a new set of vCards from .CSV files using a 3rd party application.
This week I did the monthly process AND installed an Apple Security update. I think the problem arose after the security update
I am running the current version of Mojave on my iMac
Contacts shows all the replacement vCards
However if I enter a name of one of the vCards in an Apple mail message the Mail application does NOT see ANY of the vCards as an option to complete an address field.
Any suggestions? I am planning to delete the vCard group and re-import as first attempt