I just spent 45 minutes getting 840 cryotic and 600 points. On EARTH (I'm MR17). Why so long? Why so little cryotic/points? Because these missions are bugged.
Excavation missions require you to kill enemies carrying power cells in order to fuel the excavators. In a normal excavation mission, you can sometimes find yourself with far more cells than you could use (which is fine).
Void fissure missions will regularly spawn void fissures, which will themselves spawn corrupted enemies that are not drawn from the map's spawn table, but take up spawned enemy slots nonetheless.
And therein lies the problem. The corrupted enemies spawn too rapidly, preventing the level's normal mobs from spawning - thus preventing enemies from spawning with power cells. Thus nearly completely breaking the Excavation mission type.
I only say "nearly" because the map does manage to sneak in a power cell enemy every once in a while, and there is a "workaround" (next sentence), but this is ridiculous. In the last 10 minutes, I just gave up and went from excavator to excavator, spawning them, then leaving them to be destroyed to get my 20 cryotic. This was faster than defending empty excavators and waiting for power cells to spawn - which would take multiple minutes, even while killing enemies non-stop. But this is far from ideal, as I then don't get the AABC rewards, since the excavators never actually finish. And I have to assume that this isn't the way these missions are meant to be played.
Fix: guarantee a power cell enemy spawns every X seconds, with some variation. Or multiple increasing chances staggered over time. Or make their spawn mechanic independent of void fissure-spawned enemies. Or something. But this needs to be addressed.