So, I've noticed that one particular user is showing up with CNF:longstringofnumbersName in all the AD Security Groups she belongs to.
For example, if her name was Jane Smith, she would be listed as CNF:9s383flksjf-3422-2342-23d-dfklaj9se34JaneSmith (not the real string of numbers).
This is showing in all of the groups she is a member of.
We are a single Domain with 2 DCs (one local, one in a DC). We sync with M365 using Azure AD Connect. We used to be in a hybrid environment, but are no longer. This was showing up prior to decommissioning the hybrid. Not sure that is relevant, but wanted to make sure it was known.