Have a look at the library function (although I think it is not really necessary for only 24k files).
Also see the filter
e.g.
artistsort PRESENT
There are no "empty" fields. A field with no data is simply not present.
If MP3tag really stopped after just 3,500 files then I would check the files for integrity. I regularly treat thousands of files without any problems.
Here is a thread with links to utility tools: