To let you know, Spotify has a limit of about 10,000 songs per playlist.
While some playlists can have a little more but often less than 11,000 songs, it's a bug, and some songs could then be not well displayed (or randomly) if you have more than 10,000 songs in your playlist.
That's why we recommend you keep your playlists (whatever music service you use) as small as possible and always less than 10 000 songs.
This size limit is already very high, and most streaming music services only support up to 2000 songs in a playlist...