When I am inside a playlist of the iPhone Spotify app, I can't search. When I click in the filter box at the top, the keyboard appears briefly but when the screen finishes updating, the keyboard disappears. If I double click my home button and switch to another app then do it again to switch back to Spotify, the keyboard is sometimes there as long as I was on the filter screen when I switched out of the app.

I can search from the search screen by clicking the magnifying glass without issue. That searches the whole database so it's not a good solution. On an Android phone I can search within a playlist fine. I think this started happening in the last few months.