The Russian lucked out, re Avdiivka - a weather overcast frustrated Ukraine drones and Ukraine anti-air response.
So Russian aircraft were more able to deliver ordnance.
Now, Russia supplies the overcast.
I heard that the Russians also had a map which showed an old tunnel that ran under the town. They were able to sneak some troops through the tunnel and takeover a major Ukrainian outpost on top of a hill overlooking Avdiivka. From there they were able to provide cover fire for their other troops attacking the city.