Merging Playlists Not Working

I would like to merge 2 playlists from a custom playlist that I have built on my Apple Music account. When I select songs in the one I would like to move 'Apple Music Indie' and drag them to the one I would like them to be part of 'Apple Music Alternative', I get prompted to choose between skipping or adding duplicates. When I select 'Skip' to not create duplicates, one song from Apple Music Indie is added to the second playlist. Apple Music Indie has not lost any songs. This also happens when I select all songs and right click, select Add to Playlist and select Apple Music Alternative. This method is outlined in this article:

Create, edit, and delete playlists in Music on Mac - Apple Support

I am using a PowerBook running Big Sur 11.6.5.