Blur effect disappears when zooming

I have an issue with applying blur effect.

I want the background of my scene have blur effect to distinguish it more from my main scene. But the issue is that the blur effect disappears when zoomed in too much. This applies to rendered camera movement and just regular zoom-in while working.

I tried to apply effect to the whole layer, to symbols on it - no difference. The only thing I noticed that scaling the symbol down lets you zoom-in more until the effect disappears again.