As said here: https://code.wildfiregames.com/rP22428#inline-3620
Units move the InitPos of the heard to the last known position when going through Order.Gather, which they do multiple times when hunting, thus making them mistakenly move the herd position and unable to find it back.
See the attached replay:
Without this fix, the 6 archers become idle at the CC.
With this fix, they correctly remember the herd position and hunt there.