So i did so more testing.
I found out that this bug has to do something with the location.
For example: When i place the Nanite mesh at 0,0,0 in world location, everything works fine and the mesh does NOT disappear/pop in.
But when i place the mesh at 0,200000,0 in world location for example , then this bugs start to occur and the mesh starts to disappear when i move away with the camera.
So it seems that Nanite gets some problems with meshes that are placed further away from world origin.