I saw something rather odd (and I'll have to see if I can replicate it): I attacked a Kraxis army that I froze next to my outpost, still supposedly under the effect of tremor (in that I cast it, then clicked the turn button, and assumed that they would be immobilized for one more turn although the counter jumped straight from 2 to 0).
Right as it shifted into tactical battle, the Kraxis army moved onto the outpost from the adjacent square. I defeated them, but the outpost was still destroyed. I rage-quit around that point so there should still be a save game from before, I'll see if the problem is repeatable.
It doesn't help that the AI players use the Tireless March spell (one I have never yet unlocked myself) with such great enthusiasm so they're faster than me anyway - but if they get the chance to complete an attack on an outpost even after I have intercepted them, that seems like an unfair advantage.