Since the update I have been getting serious issues with sound levels being far to low. I have turnt of sound eq. This gives a slight boost but still only about what other music apps are like on 6 to 8. Turning on eq then pushing all bars to +15 db is lower than no eq (go figure how that's even possible) Using a sound booster app works with other apps. Attempt to use them with spotify it will actually Lower the sound.
It feels like spotify is forcing how loud I can listen and any attempt to increase past a certain level will lower it's output. This is proven by sound boost apps.
I'm using a Note 3 and haven't noticed any volume issues with it. I don't use spotify's audio effects as the volume is affected, no matter what you set the equaliser to. Do you have Adapt Sound turned on for music?