As the problematic files are falc files, see e.g. here:
There are some more threads about this problem. They all end up with: Windows problem if tag fields exceed a certain length.
Also consider to update to the latest MP3tag version and rewrite the files as there is a problem with the picture position:
CHG: VorbisComment block is now always written before Picture block for FLAC as a workaround for an issue in Windows. (#53554)