We've moved your post to this help board as it fits better its content, and this is not a normal behavior of the app.
We checked this from our side and found the back button is still there. Would you mind running a clean reinstall of the app? This one is more thorough than a regular one and can be helpful to get rid of any cache that might be causing trouble.
If this doesn't do the trick, please send us some screenshots showing what you see on the app. Also let us know the operating system and Spotify version you're running.
We'll be on the lookout.
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