Im using Unity 5.3 and suddenly my buttons stopped working on the Editor (all of them, every scene) without changing anything related with the canvas. They work for Android though.
I checked there’s no panel on top of them, they have their raycast activated, there is one Eventsystem on the scene… As I said, nothing changed with the canvas.
Restarting my PC would allow me to click buttons for the first or second time I play the editor… but then it just stops working.
Edit: Using Windows 8.1 on a mac mini