Could be the update of the iOS app that was released yesterday. We recently noticed a bug where having certain special characters in your password would cause the login to fail. This was resolved in yesterday's update. So perhaps your phone updated the app overnight and it got resolved that way.
Developer of the app here, a minor correction on what Dan said above:
The app saves your progress between closing the app and the next time you open it, the website doesn't. Unfortunately we can't add this to the web interface being used there belongs to the software that we use to manage the...
That's weird. I've only heard a similar when people were using the old app, but not with the new one we launched last year. Any chance you can post a screenshot of the app you're using to make sure it's new one?
Links to the store pages of both apps:
Android: https://play.google.com/store/apps/details?id=fm.afterhours.player
iOS: https://apps.apple.com/app/ah-fm-electronic-dance-music/id6502718796