This is pretty early in the first campaign and SUB1_2 is the mission where you pick up the artifact that unlocks Mortars and the first one before you come into direct conflict with the Paradigm. However, having returned all of my units to the Landing Zone nothing's happening. I built a few defensive towers and walls around the LZ because I remembered that if you don't the LZ will be compromised, and I also lost one of the original units I sent (I didn't bring any reinforcements and pretty much stomped the rest of the mission otherwise).
There's no visible errors other than some that have come up during the destruction of Scavenger factories (I guess because I happened to time it when it was trying to spawning a unit since it didn't happen 100% of the time)