Rounded playlist art on iOS but not macOS

I have a bunch of custom playlists with custom cover art. Most of them show rounded corners for the cover art. However, some of my playlists show squared-off corners for the cover art, but only on macOS. On iOS, all the cover art shows as rounded, which I assume is the way they should be displayed on both macOS and iOS.

Could I have done something different for the few playlists that show squared-off corners on macOS? All my cover art comes from the same source, so they should all be in the same format I upload a majority of my cover art from macOS. I was thinking it might have been based on when I uploaded the cover art and that the older ones might be the ones affected, but that does not seem to be the case.