This is due to the discrepancy on how to handle the situation of partial success in enumeration(meaning some sites return success, but some return failures), initially we decided to show end users as much as possible, thus in your customer deployment, the user vdi were enumerated even though the enumeration in other DDCs(where user logon is not allowed) failed. But later we decided to at least prioritize the authentication failures, that’s why it fails the entire enumeration.
So with 3.12 the behavior of adding all DDCs for user to logon is expected, if that’s not acceptable, you can suggest customer to configure user mapping, so enumeration for a particular user shall only contact specified sites/DDCs.