When you place a Cover on either side of the Reactor Core, that Cover also appears on the inside of the opposite wall. Although it is not visible when looking at the outside of the wall.
When installing some Covers on the bottom side, extra elements appear that cause Z-fighting.
Gaps in places of perpendicular connection of textures. This can also be seen in previous screenshots.
Correction to the second paragraph. Z-fighting can occur when the Cover is placed on any side other than the top.
Yeah I guess I messed up with the whole Cover thing on this…