It appears that the Concert hall sound effect in the Equalizer menu persists outside of the app.
If I play videos from youtube/facebook/gallery for example, these videos gain the reverb effect also. If I disable the effect in the Spotify app the issue goes away.
I am running Spotify version 18.104.22.1681 armV7
on a Samsung Galaxy S8 (SM-G930F)
on Android version 7.0 (3.18.14-11104523)