I have encountered a UI bug that prevents offline access. I often travel by Airplane, and to rural areas where mobile internet doesnt really work. Spotify will randomly require that I "sign in with facebook" upon app startup.
I feel like offline content should always be available somehow, even when one can not "log in"
I have the same problem as you, the app can play offline mode when i have logged in through internett, but when i dont have internett access and quit the app, I have to log in but I cant... because i need internett access.. hope there is some sort of soultion for this problem its very frustrating when your paying for a product that wont even work. -.-
I have found a temporary workaround. If you figure out your spotify username and password from the settings page of the spotify website (the username should be your Facebook email) and log in to the mobile app using that, it does not require log in after app restart.
Not the prettiest of solutions, but it seems to work.
Okay, here is a fix I have going off a previous comment. For now, the best thing to do is to login to your mobile device using "Spotify Details", not your Facebook account. Now, for the username part, you need to log into the Spotify website and look for it. Do so by logging in, going to the top right corner of the homepage, and clicking your name. When your name is clicked, you will see the option "Edit Profile". Click on edit profile, and then there should be an option that says "set password for your devices".
From there, you will be prompted to ask Spotify to send an email containing your mobile username, (for me it was just a 10 digit number) and a link that allows you to set your password. Follow the instructions and then you can log into Spotify with your mobile device using your "Spotify Details" and the new password you set.
Hope this lets you enjoy your offline playlists when you're actually have NO INTERNET!