Slitherine

On the map for the Battle of Moscow there are silver stars on some hexes. When a unit lands on one of these hexes it disappears from map and I don't understand why. I included a screenshot and highlighted the hexes in question.

This is a neat feature of some of the SC scenarios. Your unit isn't actually gone, instead, it is now back in your reserve unit list. The advantage to this is that you can "withdraw" a damaged unit from the battle & repair it in between scenarios. The repair between scenarios will be at a lower prestige cost for elite replacements or free if you use green replacements. Additionally, once you withdraw a unit, you should then have a deployment slot open. You can therefore deploy another (hopefully undamaged) unit from your reserve or purchase a new unit to fill the vacated deployment slot. I like having these "exit" hexes as they allow you the flexibility to tailor your force mid-battle. Hope this helps & good luck.

How did you get a 13-strength KV-2 in that scenario?