I organized and cleaned some files to be used with my Traktor S4 device. I ran the Traktor software that read the tags and imported the files. I closed Traktor. I opened MP3Tag and I noticed that some filed had lost all the tags. I checked with a binary readed and I saw the tags.
Then I decided to try to repair the files and at first I copied one directory in order to keep the original file. I loaded the new directory in MP3Tag and all the files were OK. I switched many times between the two directories and the differences between them remained.
I binary compared the pair od files with the same name and they are identical.
I cannot imagine a reason for this.
I attach two screen captures.