Copying to flashdrive removes replaygain

I've set up a new PC using the same MP3tag 3.12 as my old PC. Old PC MP3Tag works fine with all my ripped mp3 files. If I copy mp3's to a flashdrive and try to read them on the new PC, there is no replaygain. As a test I wrote the original files as well as the same files that were on the flashdrive to a CD and looked at both sets on the new PC. The files from the flashdrive did not have replaygain data but the original files still did. Any ideas why this might be happening?

Do you read APE tags on the new PC?
See Tools>Options>Tags>Mpeg

I unchecked all APE, it didn't make a difference. I just noticed that the song titles are missing also.

The other way round would be better: read APE tags
Some programs store replaygain in APE tags.

Tried it both ways. No difference. Thanks anyway!

Could you load the files from the tumb drive into MP3tag and filter them with
%_tag% HAS APE

If there are no APE tags in the files (any more?) then no files should appear in the file list.
If there are still some files (or even all of them), then try again.
After you have modified the setting for reading, you have to re-read the tags to see the effect.

I also wonder what role MP3tag could play in an action that takes place outside MP3tag, completely beyond the control of MP3tag: copying files to a storage media and reading them on a different computer.

Thank you for your help. It seems the problem was either the flashdrive itself or the copy procedure. I went back to square one, formatted the flashdrive and only copied over 1 folder. On the new PC I added that folder as the only directory and everything showed up as it should. I will experiment some more later, but as of now MP3tag seems to be working properly.

It still remains a miracle that copying files should selectively remove individual tag fields.
Anyway: if it works ok now - great.

The MP3 file sizes were slightly different also. But it seems OK. Onward!