canvas elements is not visible in camera preview

Hello,

I am very new to unity. I am working on already developed 2D game. I added a canvas and few buttons over it and wrote a small script. We use source tree for versioning. After I committed my changed I noticed a graphicsettings.assets file being changed. Later, the camera preview shows no GUI elements when game editor window is resized as show below.

Please help me address this issue and also I want to what factors this change? is it graphic settings.assets file as i assumed or something else?