I can't see it being the app or phone, might be worth giving support a shout and see if there's something in the back-end whcih is causing issues accessing your account?
You can contact Spotify Support using the form here.You will get an automated reply at first, however if you need to chase them just reply to the email as it does get monitored.
I currently have the same issues on my OPPO F1s.
Before I also had the exact same issues on my Galaxy S4. I Tried clean installs and that sometimes worked for a while, but it happens again.
I start to think Spotify is just bugged, and am open for good alternatives.