Check your tags on the server for Artist and Album Artist.
This.
The sequence is probably more like:
1. Restore library.
2. Verify in the standard view (on the JRiver server computer) interface that everything is ok.
3. MC, using the information from the restored library, recognises that the files have changed, by the date and time.
4. MC Auto Import updates the library with the Artist from the tags inside the files, changing the "M" artist to Tom Petty, because the setting "Update for external changes" is selected.
5. Connect with JRemote. JRemote shows the updated Artist information, correctly. But of course the wrong Artist.
6. Go back to MC on the main computer, which has now refreshed the view you looked at before, and now it is showing the incorrect Artist.
You could test that theory simply by restoring the Library, then waiting for a while, and then refresh the View to see if the Artist changes.
Or you could just look at the "Tag Dump" area of the tag window, and see what is actually in one of the problem files. I think you will find that the Artist in the tag dump area is Tom Petty. Which is why I suggested running run "Update
tags from
library"
If you don't have a "Tag Dump" area in the tag window, search the forum for "Tag Dump" and you will find instructions for adding it.
To fix, make sure that "Options > General > IMporting & Tagging > Update tags when file info changes" is selected, restore the Library, immediately turn off Auto Import (uncheck "Options > Library & Folders > Auto-Import > Run auto-import in background") so that the setting "Update for external changes" doesn't change the Artist again, then run "Update tags from Library".
Or just fix the problem tracks in MC, with the setting "Update tags when file info changes" turned on, and MC will update the tags in the files. The problem shouldn't recur then. Unless, of course, it is some other software that keeps updating the tags in the files.