Like everyone else, I'm only expressing an opinion, but from a defensive point of view, there are fundamentals that we just aren't doing properly.
Boab mentioned a couple of pens and as couple of belters from outside the box and that can happen to anybody, but the penalties were conceded due to poor defending and the belters were due to us inviting them to have a free hit without any challenge.
The first issue is the most obvious. We defend far too deeply. The insistence on playing from the back now sees our defence shaping up to receive the ball from Barkas as far back as the 6-yard box. That means the back line don't advance as a group and that they are shapeless and strung out in various areas looking to receive a pass instead of keeping their shape.
The second problem is that our centre-halves don't play as a pair or trio, they get dragged into positions they don't really want to be in while they cover full-backs playing in advanced positions. Ajer is particularly bad for this and then tends to lunge into challenges which happened twice today, one of which led to the penalty. Duffy has presence, but a big part of his role now is going to be organising that back-line and to manage and hold our shape.
The third factor is purely down to Broonie playing far deeper to compensate for the natural loss of a yard of pace. This leaves gaps in midfield which can be exploited and the belters from outside the box would be meat and drink for a prime Broonie who would be up in their grills instead of languishing inside the '"D". Lenny done something similar in his last season as a player with us and it was as noticeable then as it is now.
It's fine to play from the back, but our starting positions still have to be further up the defensive areas. Any halfway decent player will punish the space they get to play in when our centre-backs are barely up to the penalty spot.
As far as the full-backs go. The best example is the Liverpool model. Trent-Arnold and Robertson are encouraged to get forward and get balls into the box from higher up the park. Every time they do this though, there is someone to cover the gaps they leave. When teams play narrow against us like Livi did today, that should leave us space out wide to play in, but often our wide players and full-backs are just closing their own spaces by being virtually on top of each other.
This is all pretty basic stuff and easily fixable, but we will lose quite a few goals this season if we continue to be as shapeless as a Castore school jumper. The need to be on the front foot in games should never detract from sensible and solid defending. In the vast majority of our domestic games, Celtic need combative midfielders, but not necessarily holding midfielders. I think Lenny might be doing the captain a disservice by using him so much and he should pay heed to his own final season in Hoops and how he himself was often the brunt of the fans frustrations.