3 CB defence is messing up our assignments in the box IMO.
If you look at the tying goal, Ogbonna is in line with Caceres who is the other CB. The player is offside if Bonucci is not on the field. The 3rd CB complicates the box assignments to me because he's in behind Ogbonna's man and keeping him onside. For Ogbonna, he's thinking either his man will be offside or if he's not offside, at least the sweeper, who is marking no one, will slide over and pick him up, since he's keeping him onside anyway.
For me, there's a problem when the sweeper is a free man but he does not ATTACK the ball. He just complicates the scenario in the box. I think with only 2 CBs, they take their marking situation more seriously, they are not trying to slide in front or form some type of partnership with the sweeper, they are just muscling their man and attacking the ball.
I feel on set pieces our CBs are always looking around at each other like it's someone else's fault all the time. Actually both times, the goal comes from Ogbonna and Bonucci looking confused.