I'm seeing the same issue on 1.17 - SOME users must put domain\id in order to login.
This is odd because I have not seen this issue before on the old server (still running 1.11)
My environment is this. I setup a new Ubuntu 22.04 Server VM and installed the latest 1.17 release, brought over my DB from the old server, and the 1.17 DB upgrade succeeded. So I configured the LDAP plugin just as it was configured on the old osticket system (which was on a Win 2016/IIS server). However, some - not all - users are not able to login unless they specify the domain name.
Once logged in, users can see their old closed tickets, create or update existing tickets that came over with the DB import, etc.
Looking at their accounts in the directory, I don't see a difference from a user that does vs a user that does not need the domain\ for logging in.
Everything in v1.17 seems to be working great, but I have yet to make this the Prod helpdesk due to this domain login issue. So I'm still hitting it via IP instead of intranet url.