Hey there @tord00,
Thanks for reaching out about this here in the Community.
First up, we suggest that you head over to the app settings on the desktop app > toggle on Show Local Files > toggle on all the sources that appear there.
Additionally, could you go to the settings of the Spotify app on your iPhone, scroll down to Local Files and make sure Desktop Sync / Local audio files is enabled?
If the issue persists after following those steps, it's well worth running a clean reinstall by following these steps on your devices to see if that helps.
Keep us posted on how it goes.
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“Music acts like a magic key, to which the most tightly closed heart opens.”– Maria von Trapp