iTunes will not save song data edits

For the past six months or so, my iTunes (v12.9.5.5) library will not save edits to music files. This includes song titles, artwork that I add, track numbers, genre, etc. This happens when I try to edit single files, and groups of files (e.g. an entire album). Sometimes the edits appear correct, but then revert to the original. I'm using MacBook Pro (mid 2014), and OS10.14.5. I've never had this problem, on any version of iTunes, any Mac, any OS, until recently. Grateful for any advice to fix this.