You're most likely expecting the behavior of the Windows version, which I've decided against for the Mac version. It's an endless well for lots support questions and one of the non-obvious features that got stripped for the Mac version.
It is becoming little cumbersome and risky to import tags.
My process is exporting the _path with tags for conversion.
Data conversion needs a lot of sorting, redo, curation of data, This is done one field at a time, Album, Song Title, Singer, Composer etc
this takes few weeks and months.
After the data conversion, I want to apply the new tags to audio files
When I am ready with new set of data
I open the audio files in mp3tag
I export the audio file list with _path to get the order of songs in the mp3tag in the current session
I use it as template, add new tags columns to it, with vlookup on conversion data.
use this “_path, new_data” textfile to import tags to audio files
This is my process defined now. But we should be able to avoid it. if mp3tag can search for the tags.
When everything is working smooth, it looks COOL
if by chance, we sort the songs in a new order while preparing the textfile or something out of ordinary happens. We apply wrong tags!
If you are already doing this process manually, and with so much effort, why not do so within mp3tag to begin with? If you require a text file backup, you can generate that with an export from mp3tag afterwards.