some of the songs downloaded are not playing offline (while most do)?

[KatesHere]

Hey there @Gille, welcome to the community!

That sounds very odd. Does it happen on all the devices you use Spotify on? Try a clean re-installation and see if it helps. You can find how here. Keep in mind that after that you'll need to download again all your offline content.

Let me know how it goes 🙂

K