On iPhone the volume will be maxed out everytime you watch a video.

[Trapjackson]

If you’re playing music on a device with your phone and try to view anything with sound like a video or someone’s snap on Snapchat it’ll be max volume practically every single time. Very rarely you can watch a couple snaps in a row before the volume maxes out by itself. And usually when you try to turn it down it’ll turn your Spotify music down too. Extremely frustrating and annoying. I’m not a fan of not being able to essentially use my phone when playing music bcuz my ears can’t handle my phone screaming at me when I watch a video when I’m doing paper work or something that pertains to the video. Not sure if this is Apples bug or your guys’ but i don’t remember it being like this until a few updates ago. 

[Loxer]

Hey @, welcome to the Community.

Hope you're doing great!

Could you try logging out of Spotify, turning the device off then waiting a couple of minutes before switching it back on? Try to log in to Spotify to see if that makes any difference.

If that doesn't do the trick, try a clean reinstallation of the app by following the steps here. 

Keep me posted 🙂