There's a couple of issues.
Lack of Midfield protection.
- Busi and Rakitic make it so easy for teams to cut through both of them because they are slow as fuck and don't exactly have the high-quality energy to make up for it like they once did. Busi relies on his technical ability with the ball and his brain to make up for his weakness in terms of pace and physicality. While Rakitic relies on tactical positioning but despite that the two are weaklinks in the Midfield when it comes to defending these days.
The Elephant in the room that is Pique. Roberto has problems with his defending and Semedo has flaws going forward but, Pique on the other hand fucking hell. He plays like someone who doesn't have his head in the game and is slow and terrible in 1v1 duels. the only thing really saving him is his ball playing ablity and his defensive headers.
People like to give Umtiti shit sometimes and while some of it may be justified there's no question at least in my eyes the dude is carrying Pique Hard. If you want to play Roberto, you are going to need a better RCB who is comfortable defending in 1v1 duels and wide areas. If you want to play Pique you're going to have to play a more defensive RB who has the pace to help get back in time to help him out.
The funny thing is our problems with the defense and Midfield are usually down to the Vets and not the newer players.