I hate to see that happening to you as well. Many other people are facing the same issue even with newer models. I think it might just be a bug that is causing that and I would be fixed in the next update.
In the mean time, you could try to reset your phone through iTunes, it will do a miracle to your device by removing all the junk and stuff being added up in the OS that would make it fail and make issues like this one pop up more often.
Another tip I would give is to close some apps in background that you aren't using but are just staying there. I know Apple says the opposite but when you aren't going to use them right away or the next few hours I don't see nothing good coming from keeping them open in the background. Limit the background app refresh because I am sure you don't need all the apps that support that to be constantly being refreshed in the background except for the ones you really need to.
Part of the big problem is also iOS 11, which boy was it buggiest one Apple ever released.
However as I mentioned above, the next update of Spotify should fix this.
Hope it helped, if it did mark it as a solution and drop a like!
LoxerRock Star 16
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