The number of enemies per room is chosen somewhat randomly, yes. We have a "difficulty" rating as well that increases the possible number of enemies based on how many items you have bought from the store, to make the game more difficult as you progress. This was rushed out at the end of the jam, however, and probably needs to be re-balanced.
The problem where the vision cone is not visible is probably because the enemy is outside of the camera view, so the game object is culled. This was a bug I noticed too late to fix, because I didn't playtest the enemies enough :/
Glad you liked it :)