NOTE: requires mods, ability to manage zip files and (temporary) cheat mod. | Works as of Jan 2025
I ran into this issue in Jan 2025 and was first real problem I've had w/game. I read all the posts saying you had to restart (the game application itself and the entire mission) to fix the mission bug where the horde never spawns. I was going to be super pissed if I had to do this so I found a way to avoid it. Do everything below at your own risk, etc etc - but it worked for me.
A) You ran into the mission bug where horde doesn't spawn B) You have no closed your game or restarted mission yet C) You killedthe Reacher guy already D) You know how to zip files, backup files etc