- Check the tags for track 7, you will find that the name is different somehow. It may have a lower case letter instead of an uppercase letter, it may have an extra space, a space that is not a space or an incorrect foreign character, but there will be a difference somewhere in the tags compared to the rest of the album. If in doubt, use copy and paste wherever possible. :)
- There seems to be a problem with your tags or with Plex. The Artist names should not end with .... and you should not search for .... That might be a problem with foreign language vs English perhaps? Or maybe it's just because of the small window size?
If your Artist names were complete and not truncated, then you should not have any problem searching for tracks by artist. Remember, Plex does NOT use the Artist tag to gather the Artist name, it uses Album Artist to gather the Artist's name, but you should have both the Artist and Album Artist tags in all of your files, except where noted.
In all of my Various Artist albums, I do not have any problem searching for a particular Artist. Also, all of my Various Artist albums are in a library of their own, although that should not make any difference.
For your logs, you do not have debug logging turned on, so they are next to useless. :(
Also, these are the only fields you really need to fill in, the rest should be blank, but that is up to you of course.
Artist (for ALL tracks)
Album Artist (blank for Various Artist albums, filled in for everything else.)
For music files of unknown origin, it is a good idea to remove ALL tags and then write your own tags into the above fields, that way, you wont have any badly formatted tags or useless comments which can sometimes cause issues.
I use Tag & Rename, because it makes the whole process very easy and allows you to copy the tags you want to keep, and then write them back in when you need to. Very useful for saving the track titles after wiping the entire tags for an album for example. I'm not sure mp3tag can do that?