From my experience, this tends to happen right after that big fight with Ward soldiers near the D2 entrance where Korshunov and Dr. Dalin are supposed to show up for that important chat. It's actually a pretty common issue that's been giving players trouble, but there are a few ways to get around it.

The quickest fix is jumping into developer mode and typing XTeleportNPCToPlayer Korshunov in the console, but I know not everyone's comfortable with that stuff. If you'd rather keep things simple, try loading a save from before that whole Monolith encounter started. Sometimes the game gets weird about spawning important characters if there are still Ward soldiers hanging around, so make sure you've cleared them all out properly.

Something interesting - the game can get confused with all the faction stuff going on, so if nothing else works try spending about 24 hours in-game time away from the Garbage and Industrial areas. That usually helps reset things. Most players have good luck just reloading an earlier save though, which is why I always tell people to save often especially before big encounters like this.

If you're still having trouble, make sure you've got the latest v1.2 update installed since it fixed a ton of these spawn issues. And while it might be frustrating right now, don't worry too much - you won't permanently lose access to any important stuff like the Projection Room or Dubny's research, it just needs a bit of fixing first.