Conside loading everything up in MP3TAG in large batches. (www.mp3tag.de)
Use this to delete the rogue MBID fields.
Do a MULTIPLE select of ALL files in the list.
Hit the ENHANCED TAGS button and now you can DELETE ALL MBID tags in one go.
MP3TAG is great to use alongside Picard.
Picard for identification, MP3TAG for bulk operations on lots of files.