
This section is
not sorting - it is grouping. MusicBee uses these fields to define what is an album. For example, in the above image, if the Album Artist and the Album are all the same over a set of tracks, then MusicBee will treat all these tracks as a single album.
You are adding 'Track Count' to this list. Track Count is the total number of tracks on an album (not the track number). You can check this for any file by right-click on that track > Edit:

The highlighted area (Track 02 of 11) shows the Track No (02) and the Track Count (11)
Since your album is being split when you are adding this field then you must have a different value of Track Count set for this file when compared with all the others.
The files you uploaded were fine, and you say that you deleted everything in Mp3Tag, so I can only think (as Steven suggested) that you have not rescanned these files in MusicBee. To do that:
Select all the tracks of the album > right-click > Send To > File Rescan
Sorting:I'm not sure that the Sort By setting is an issue here, but Steven was referring to this:

(and this is how you set the sorting on a particular view)