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