Kuva Siphon Exterminate missions don't spawn enough enemies.

[Braneman]

Oftentimes when doing a Kuva Siphon Exterminate mission enemies will stop spawning entirely, sometimes more than 100 enemies away from the objective. So what has to be done is walking back between empty rooms and the exit to get enemies to spawn 1-4 at a time to finish the exterminate mission. This is not a surefire method to get enemies to spawn, so if you're even 30 enemies short you have to spend that time bouncing back and forth between rooms for upwards of 10 minutes doing nothing.

During the mission you'll often find lots of rooms with nothing in it just empty rooms and more empty rooms until you reach the Kuva Siphon.