If you accept a manhunter quest and the temperature drops low after that (the treshhold might be -60°C), the manhunters will not show up after the noted time. If the temperature rises again, they will still not show up and the quest seems to be stuck (with the temporary soldiers).
I was made aware of this issue by this: https://steamcommunity.com/app/294100/discussions/0/5015323029415846940/
I generated a manhunter mission with helpers, accepted them and then made sure the temperature is very low through coldsnap and climate adjuster sites.
Here is the save with a counter a few hours before the manhunters should arrive: https://easyupload.io/v1470z
Both DLCs, no mods used.
Somewhat complex. I will not look into this.
Thanks for the bug report, I was able to reproduce this in 1.3.3242. I really appreciate you providing that save, it has general conditions that are good for testing this. I'll be bringing this up to the devs.