Spotify Editorial Playlists -- How are Dynamic Changes Determined?

[SoundGuySays]

I recently came across the Spotify-curated playlist titled 'Thrifted'.  I started listening through this playlist quite a bit and became familiar with the track listing.

At one point, I attempted to queue up a song I knew to be included in this playlist, but upon manually scrolling through the playlist, discovered that the song had been removed.  A few days later, that same song had reappeared on the playlist.  Then, a few days after that, the song had been removed again.  I've come to realize that there are a handful of tracks on this playlist that get dynamically phased in and out, while other tracks are static and are always present.  

My questions are -- How are these editorial playlists maintained?  What causes some tracks to come and go?  Is there a way to influence the editor(s) of the playlist to keep certain tracks on the playlist?

Any insight would be appreciated!

P.S. -- The track in question is 'Breadcrumb Trail' by Slint.  I had actually never listened to Slint before discovering them through the Thrifted playlist.  I subsequently fell in love with the album on which Breadcrumb Trail appears, and now I'm woeful the track is no longer on the Thrifted playlist.