We can see when we rotate the device the shadows are dispearring from the bottom to the top which clearly means that is related to the angle of the camera.
I face the same issue here. I got dynamic shadow enabled on my movable object using stationary directional light. The issue is exactly the same if I also use movable directional light.
This seems more related to dynamic shadow for mobile device issue.
Have you tried playing with the Dynamic Shadow Distance value on the Cascaded Shadow Map tab on your directional light? If you haven’t, try to pick the values that could remove the issue. I had the same issue and I tried around 2000 and it worked.
With only a static SkyLight and a Stationnary Directionnal Light, built the whole thing with cascaded shadow maps. It seems to work. But I used World to Meters. and the limit is to short
It looks like UE bug. even if i set 80000.0 distance. From some angles shadows apears, then rotate person and camera and shaows disapear. It is looks same is and on UE4. If enable Distance field shadows and in Cas shad map Din Shadows Distance set to zro. Then no isues but it working only with static shadows looks.
Or if set num Dynamic shadow cascades to 1 then also no isues. but now other problem. Now small objects (main person for example) not have shadows.