Enemy champions and minions appear invisible when they definitely should not be.
I was playing as Rek'Sai and would get the visual procs of tremor sense in locations that were not in the fog of war. I figure that the bug is either that units are appearing invisible when they shouldn't or that the map is showing up as out of the fog of war when it is actually in the fog. Here are two screenshots I took from the replay tool. You'll notice that the enemy team does not have any champions with invisibility/camouflage mechanics: