Spooky duplicates in CiviCRM
The ghost story goes like this:
Duplicate records are not usually a major headache on your site, but one day you find a collection of dozens of duplicates contacts that contain no data, except an identical email address.
Baffled, you merge all those duplicates and double-check to be sure they're all taken care of.
A week later, you find another dozen duplicate contacts in the same situation: they all have no data except an identical email address.
Rinse and repeat. No matter how often you merge them, they keep coming back.
What the heck is going on?!
Nope, your site is not haunted. There are no ghosts.
This frustrating and mysterious behavior gets reported now and then, in a few different places in the CiviCRM community. You can find it in the CiviCRM Stack Exchange, in the public issue queue, in the MatterMost chat logs.
The explanation is not simple, but I will simplify:
The linkage between your CiviCRM contacts and your CMS users is corrupted and needs repair.
It may not affect all your users, but it's clearly affecting some of them. And every time those users log in, CiviCRM creates a duplicate record using only their email address.
This is one of the dozens of common issues and I scan for in my CiviCRM Diagnostic Scan. I've seen it come up on several sites, one just recently.
The fix is also hard to describe, but pretty simple from a technical viewpoint: We just need to identify the users that have this problem, and repair the link to their CiviCRM contact.
No ghosts. No exorcism.
Everything happens for a reason. And once we find the reason, the fix reveals itself.
All the best,
A.