User vanishes in System preferences- Screen Sharing

I have a iMAC 2012 running Mojave. I regularly used back to my mac to connect machines. Since Mojave no longer supports back to my mac I have setup a new system (Screens 4). This requires System preference (Sharing) changes, specifically the “screen sharing” and “remote login” to have the user added to the option. What is strange is when I add my user name to both of these items in System Preference (Sharing) and than I exit screen System Preference they vanish. That is when I reopen System Prefernece- Sharing- and look at either Screen Sharing or Remote Login my user name is NOT there anymore. As a side note on my other Macs I do NOT have this problem so it is specific to this MAC. I also reloaded Mojave onto the MAC 2012 and still experience the same issue. Last piece of information, a couple of years ago I had a conflict with user names/computer names and my fear is this has propagated to where I am now. Anyone have suggestions on what to do to fix this??