I'm getting some (maybe 5%) email address imports rejected with the message "Matching this contact based on the de-dupe rule would cause an external ID conflict" The email addresses in question can be updated in the UI without a problem, and I can't see that adding these rejected email addresses could cause any conflict. The supervised dedupe rule is 'Name and email'. What's the cause of this error? (Changing the dedupe rule to bypass the problem doesn't work so I'm thinking this might be a bug) Civi is at 5.11.0.
I had the same outcome when I imported external ID, first, last name and a physical address update. My dedupe rule only contained 'external ID'. When I removed the first and last name the import worked.