Why can't I add some songs to additional playlists?

[#1]

In my library I have 2 lists. One is all of my songs and the second is a selection of songs from 'all'. Some songs won't add to the second list and some appear to be added (green tick) but don't show or play in the second list.
For clarity, one list is all my songs and the second list is made up of my songs that I can play around normal people/kids.

[MihailY]

Hey,

Thanks for reaching out.

What device does this occur on? Please send over the device model, OS version and Spotify version. Can you check if the same happens on a different device?

Also, have you noticed any pattern in the songs that can't be added to the second list (e.g. tracks from other playlists, from the search results, from the Local files folder etc.)? If possible, send over a short video of the behavior so we can try to reproduce it on our end.

We'll be on the lookout for your reply.