Spotify stops playing when not on primary screen

[AstridClaessen]

Since yesterday Spotify is showing strange behavior: I start playing a playlist, no problem it plays.

Then I start-up any other app on my phone: Spotify stops playing and will only resume playing when Spotify becomes the primary screen again.

I'm in off-line mode, playing lists that are marked as "Play in off-line mode".

Does anyone recognize this issue and preferably even know a solution?