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. If you have more than 10,000 songs in your playlist, some songs may not be displayed well (or randomly).
We recommend keeping your playlists (whatever music service you use) as small as possible, always less than 10,000 songs.
This size limit is already very high, and most streaming music services only support playlists with up to 2000 songs.
Regarding playlist size collection, Spotify generally limits users to a maximum of 11000 playlists.