1) I'm afraid I don't know what you mean. If the server doesn't sleep while you are doing tagging, and sometimes tags are remembered (they "stick"), but sometimes they are not remembered, then I suspect that you aren't saving the tags in the first place when you edit them. But MC just about always saves the tags you have entered, no matter how you enter them. So you are going to need to describe exactly what you do (files selection, clicks, tabs, enters, escapes, etc.) to reproduce the issue.
If it only happens sometimes, you must be doing something different, sometimes. If it happened all the time, that would be easier to understand. You would just need to turn on Authentication on the MC Server, using a Username and Password, and disable "Read-only Authentication".
2) I'm going to need a picture or two of this. Are you tagging in a Panes View, with checkboxes next to Artists, or similar? MC doesn't have a standard field called "Performers", so I assume that you are talking about the [Artists] field that you are adding to, or a custom field you have created.