The Darklings weren't as unaware of Max's observations as the Arisen Army was, it seemed. Not long after he noticed their mass arrival in the other layer of space, they sent a small attack craft to block the millimetre-sized micro portal that he had opened to watch the other layer.
They didn't attack it or attempt to interfere with it. They just put a ship in front of it so that he couldn't see anything but a small piece of hull.
For a group that was known to capture and enslave entire populations, it was an ingenious trick and one that would work with regular portals as well.
If you knew where they were going to open, you could just put a ship on the other side and let everyone come through directly into your holding cells.
But though Max couldn't see anything with the sensors, he now had a much more informative source of information. The crew themselves.