The issue is discussed in this UDN:
Key quote from UDN thread is:
"Also, having made a texture array with 190 entries, it seems to partially work in an Editor build but the closest mip (or mips) are black. In the distance the texture goes it's correct colour, with the texture layer being chosen based on voxel type."
The problem occurs on both DX11 and DX12 and is not specific to either RHI.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-87063 in the post.