I'm having an issue in version 2.8 where the material in slot 2 (I haven't tested higher slots) will not render. See image:
As you can see the floor of this room (which has a different material from everything else) is not rendering at all. I know that this is caused by it being set to the second material slot, because I get the same result even if both slots have the same material.
Edit: It seems that in some cases, it will render, but slightly transparent. Either way, it's definitely not what I saw in previous versions.