Okay, this has happened to me three times where the Spotify app (android) thinks I'm offline when I'm not. I have a Samsung A5. I have tried logging off, logging in with a username and password, logging in with Facebook, uninstalling the app and reinstalling. What worked for me was to go into the Settings on my phone, under Applications, finding the app, and telling it to "Force Stop". "Yes" to the message about potential errors. Going back into Spotify and it works! I'm online again! It's very annoying though, for an app I'm paying monthly to use and it doesn't always work.
Same on S8+ with OS 7.0 on 188.8.131.524 and I have this issue for some time already... the Force Stop method works for me too. It will be quite annoying to Force Stop every time I want to search for a song and it's weird that they have not found a fix yet :)
Your solution as a spotify employee is to make sure offline mode is off? This makes me want to end my membership entirely if this is the kind**bleep** service yall are going to give us. You KNOW heckin well that so many people are having this problem on their phones and desktop. Stop gaslighting us. We've already checked to see if offline mode is on or not.