Well, I'm not a coach, but I'd take a guess the problem is declining automatisms, not formations per se. The players seem to have forgotten how to move, create space for each other and how to press quickly in certain situations. Such thing are mantained only by regular training in rondos, mini-games etc. if I'm getting it right. If the coach lacks knowledge to use these tools, the gameplay steadily disintegrates.
Obviously, Ancelotti could build a good oldschool counterattacking team, I don't understand why he hadn't done it.
Is mantaining of attacking/pressing game an unofficial part of his contractual agreement? If so, his appointment is even less logical than I thought.
Bayern does not have the matching players for it - Ancelotti tried to tell them to leave the ball to the opponents and wait on counters - but that only gave chances to the opponents. That team wants to have the ball.
It is formations, too. Or atleast playing players in the positions together who still have this automatisms together. We were playing the old 4-2-3-1 today again - the first time this season with Müller behind Lewy and two wingers - Thiago on the 8 and Vidal in midfield...
All had a fine match - could have scored some more but it was atleast a 4:0.