I think that the problem lies in album art. The first time you edit tags with MM 2.3.1 it seems to create the album art field in the songs and as such updates all tracks. It doesn't actually add album art, just prepares the song.

Try the same routine twice on a set of songs. I guess the second time you do it you'll see it's faster (seemingly skipping the songs that have no changes, which should be all of them).

MM is speedy and great for organizing large # of files.

But there is a bottleneck.

Goal: To fix flawed tags, misspelled artists, etc. and match filenames to tags

1) Retag all files from filename
2) Using Artist tree, find and correct flaws in artist names
3) Auto-organise the files to correct filenames so they match tags

1 & 2 are fast. 3 is not, because even if only a few filenames need correcting in a list of 500 to match their new tags, it insists on re-filenaming ALL the files (even if there is no change) unless you unclick each and every box. That means you wait...and wait....and...

Is there a way to "unclick" all the checkmark boxes and just check the ones which need renaming (the ones highlighted yellow) ONLY ??

Out of 52,000 files, only maybe 300 need renaming. At this rate it will take about 40 hours to accomplish that...