Hi,
It seems that Apple's GRP1 tag is not available to read/write using node-id3. Some additional info available here
To test or reproduce, opening an mp3 in apple music > right click the track > get info > update the 'grouping' field > read the tags using node-id3 and the tag will be missing.
I can have a go at making the change to add this tag but seems I need access to create the branch