#1 Puzzling lack of activity from Niko Kovac
Having a man sent off so early in the game usually means a reshuffle for any side. Even more so when you have a centre-back sent off. It seemed fairly straightforward that Benjamin Pavard would go into the centre-back pairing with David Alaba and Kimmich would resume duties on the right. However, the entire reason for putting Kimmich in midfield was to add some steel in the middle alongside Thiago.
With Kimmich moving to right-back, Thiago was left to cope alone in midfield behind Thomas Muller, Serge Gnabry and Philippe Coutinho. Despite Lewandowski coming deep to help out on many instances, Bayern failed more often than not to create much playing through the middle.
Kovac could've added Javi Martinez to the mix earlier to provide a base from which to work, but he chose to act (or not to act) with an arrogance that Bayern could potentially outscore their opposition even with one player fewer than the opposition. A decision that played a big role in a humbling defeat.