Solved! Go to Solution.
Helo there, in case anyone is still having this issue I want to comment on how I got it fixed.
Issue: When downloading albums the mobile app showed them as being downloaded and after finishing, half an hour later every downloaded song was gone, as if it had never been downloaded in the first place.
I even switched phones and this kept happening, using my same spotify user.
My way to solve it:
I noticed that when trying to download some albums, I got the "Epic collection, friend..." message, the one i got when i reached the limit of saved songs/albums.
So I deleted the app cache, uninstalled it, restarted the phone and then reinstalled it and started removing albums from my saved collection (do not confuse with the downloaded albums) and voila, since then, I've been able to download and maintain the downloaded songs.
I hope this helps someone being annoyed by Spotify's stupid bugs as I was.