Using a single directional light and deferred rendering, I find that the shadows in my (simple) scene vanish sometimes depending on the camera position and orientation. When the camera is moving continuously this manifests as a flickering of the shadows.
I have seen other similar questions in which solutions have been reported as successful involving changing Unity’s shadow-related quality settings, but none of these have had any impact in this case. Similarly, there is no reason to think this is z-fighting - which is often blamed - since the symptoms are different (shadow is either fully present or vanishes completely).
See this short video clip for a demonstration of the effect: - YouTube
Before anyone makes the obvious suggestion: my graphics card driver is up-to-date (ATI Radeon HD 3400). And in any case, shadows do not fail in this way for other 3D applications, so I am assuming I have made an error somewhere.
In the quality section, check the distance of the shadows. This can cause issues with the camera as it moves OR if the object that should be casting the shadow moves. I know this is a very old question but should someone else see this its worth a shot. By adjusting the cameras position - as mentioned in ops answer - it essentially does the same thing. By moving the object close to the camera itself so it is displayed correctly
Change Render mode of your light (used for shadow) from Auto to Important it will solve your issue.
make quality setting as Default now its will not affect to lights while light is Rendering as Important.
This just started happening to me as well. When I look away at a 45degree angle, the shadow immediately disappears and pops out of existence. If I look up above 30 degrees it also disappears. I’m reversing everything I did to find the culprit. I can’t use GI lighting above .01 because it takes longer than 8 hours to bake (even on my new i7 machine).