Lost units sometimes get disconnected from their AI group and run to the corner of the map #1517
Description
In various types of 'neutralise all targets' missions with the lost sitrep & in particular with the 'Lost World' dark event active, it's possible for lone lost units to end up being disconnected from their AI patrol groups and instead clustering in the corners of the map.
This can be extremely annoying, since by the time your units have located them, it's frequently possible that more lost swarms will have been created, turning the end of the mission into a tedious zombie-grind-fest (and possibly worse, depending on the specifics of the situation).
In some cases they can be extremely hard to find, having hidden behind a wall or similar. This will probably need some investigation & logging of the AI trees to see what is going wrong - even when the disconnected units are discovered, they don't attack or do anything so I suspect they've lost their behavior trees altogether.
Possible thing to check: Zip Mode, Zoomier Zombie Animations Mod