Depth of object sometimes fails

Its about the little 1’s in the images.
By moving the camera the 1’s move behind the plane.
The 1’s do not move, only the camera moves.
The square sizes are 100x100.
The z position of the squares is 0.
The z position of the numbers are all 1. There is no difference between the other numbers there. (higher number is closer to camera)

So my question is how can i solve it.?

Thank you!

244000-nr1.jpg

244011-nr2.jpg

I figured out it has something to do with the material.
The translucent material has this problem. When i change the blend mode it to opaque the problem goes away. But its not a solution to my problem.

Another thing. I change the height of the number from z=1 to z=100 which clearly is far in front of the plane. The problem still persists.

The numbers as well as the planes are instanced static meshes.
both materials have depth test enabled.
when i change depth test disable for the numbers the problem persists.

I am working around it by changing the material.
But right now this issue seems like an UE4 bug to me.

244511-nr3.jpg