This isn't anything we can reproduce with imported vs non-imported users.
As I said, there is nothing in the entire code that would be able to tell you who is imported vs who is not, so there's nothing at all in the code that can apply different behaviours to different users on this basis.
Realistically, this needs to be troubleshooted from scratch and that will include testing with any and all add-ons disabled, and if necessary submitting a ticket with a reproducible case and access details for the server (FTP and database ideally) so we can troubleshoot the code. In that process, if we find a bug we'll either re-open this report or fix it.