Mythic+ testing is available on the Patch 10.1 PTR once again and Incorporeal and Afflicted have received some massive spawn rate nerfs.
New Spawn Rate Logic
Previously, the Afflicted and Incorporeal spawns seemed similar to the Explosive spawn logic, that is, random spawns that scaled directly with the number of mobs in the pull. Now, it seems that Afflicted and Incorporeal may have had their spawn logic completely changed this week to spawn logic that seems to be more similar to Quaking.