I had the same problem, tried everything, even logging in again didn't work. But there is a fix!
My problem was that the buttons where all just outside of screen-space. This means that if you click and hold on the space next to the drop-down menu's, and drag your mouse, spotify will move with your mouse.
Aka -- You are not in full screen mode! You simply cant see the buttons anymore because you eather switched displays, changed resolution, or made a mistake by making it too large. Dragging spotify to the left, and resizing the screen will fix this.
I'm running into an issure on RHEL 7.1 where after upgrading to spotify-client-184.108.40.206.g8f111100-2.el7.x86_64, it launches in full screen mode and I haven't found a way to get out. My quick fix is to launch spotify with the '--minimized' option: /usr/bin/spotify --minimized &
CentOS7 here, happened to me also after I changed my big monitor with a smaller one. The config files are in $HOME/.config/spotify I deleted that folder and the application started with its window decorations as expected.
lol. in my case, the spotify wasn't called "spotify" because the window title is by the name of the song ( list all windows using wmctrl -l ). so in my case i had to run wmctrl -r "Immolation - Passion Kill" -b toggle,fullscreen. Thany you very much :D