iTunes "Add Artwork" Glitch Corrupting MP3 Files?

So I just recently started experiencing this glitch. When I add album covers, manually, to any mp3 file, itunes, will edit the file and actually added some seconds to it and repeat the end of the track. This is very inconvenient and as a DJ it's making me have to be extra cautious whilst working.

I haven't found any solutions yet except for one other article from years ago.

Any help fixing this would be appreciated. I am running Mojave and using the original iTunes for personal reasons which doesn't allow me to upgrade the OS or iTunes.