We'd first recommend trying a clean reinstallation of the app following the steps in this Spotify Answer.
In general, there are a few possible reasons why your downloads might be removed:
You've downloaded music to more than 5 devices. You can double check this here. If you see a device listed more than once, we'd recommend following the steps from the Spotify Answer above to perform a clean reinstallation of the app on that device.
You haven't been online with Spotify at least once in the last 30 days.
Tracks in some playlists are updated regularly, meaning tracks might be removed.
On Samsung phones there could be several processes which clear app cache in order to increase performace on the phone. Check that the Bixby app is not scheduling any cache clearing for Spotify. If that's the case - disable it.
You can also try the follwoing: Go to settings >Device Care >Storage > Storage Booster > Auto Delete Unnecessary Data>Turn it off.
Let us know how you get on! We'll be right here if you need more help.
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