Handling of (large) Playlists unreliable?

[JohnnyD4]

Spotify Free GER Windows 10

So heres the thing. I have a Playlist Listened_to, about 9.000 Songs. I have about 4.000 Songs in my Spotify_Favorites (the songs for which I clicked on heart). I have a new Playlist from a friend, lets call it Candidates, with about 1.000 Songs.

1) I open the Favorites, press Ctrl+A and rightclick-add add all to Listened_To, just to make sure all of them are in it. (Not adding existing Songs again)
2) I do the same with Candidates
3) I sort Listened_To by Date_added and mark all songs that have been added recently (in the last x seconds). I create a new Playlist Candidates_filtered from it
4) Browsing through Candidates_filtered, I notice that 23 Songs are already liked.

Because of Step 1, Step 4 should be impossible, right?
If I do step 1 with a new Playlist as target, the number of Songs in this new Playlist is exactly the number of liked Songs (Favorites), so Ctrl+A works flawlessly.

What is wrong here?

[CarlosE]

Hey @JohnnyD4,

Thanks for reaching out to the Community.

Performance issues such as what you're describing can occur when handling very large playlists. In these cases, we suggest splitting those large playlists into smaller ones to have a more reliable response when navigating or handling them.

We appreciate your feedback on this matter as it helps us keep improving.

Hope this clears things up. If you need anything else, the Community is here for you.

Cheers!

[JohnnyD4]

That is not a performance issue. It does not take long, it produces faulty results.
By the way: The performance issue with large plalists is there just because it is a shabby Chromium-based webapp instead of a native app. Native apps have been happily handling playlists with 10.000s of songs 20 years ago.