I had a problem with the layout of one of the lairs I raided.
The problem was that the lair had a unpassable moat right in the middle, and my troops were unable to reach the spawner to complete the mission.
I am not sure if it was intentional, but after a long time trying to complete the mission, I was able to find a single spot where my sniper was able to free-aim between two rocks to hit the spawner.
Not really a game-breaking bug, but it made the mission quite tedious…
pandorian lairs can be annoying