Unfortunately, for now, the option to share a playlist on Instagram with its custom artwork is not available. This is why you see default four-tile album artwork instead.
Further, keep in mind that the artwork that shows up instead displays the first 4 album covers that were added to your playlist. This would explain why you don't see the album covers of any new tracks you've added to that playlist.
On another note, if you'd enjoy having the option to share the custom artwork for your playlists instead of default four-tile one you're seeing, we'd suggest headinghereand adding your+VOTE.
If you'd like more information on how the Ideas Exchange works, make sure to headhere.
Hope this helps clarify things. Happy Holidays!
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