By far their biggest issue is goaltending, they have been downright bad. Their team and individual goalie stats are downright ugly and the eye test matches. Just a lot of shots that just can't be leaking through on NHL goalies. It's so deflating for a bench when they can't trust their goaltending.
Secondary issue is team defense. They rely so heavily on younger players and just don't have enough strong defensive vets to support them. Sanderson has become their best D but he's young and still a bit raw, also not yet as physically strong as he will be in his prime. Chabot is way more geared towards offense and a bit of a gambler, Chychrun never quite as good as people built him up to be. Zub is a decent low event minute muncher but they could really use a stout right shot defender to help mask some of their other issues. Their forward group could use a couple guys like Silf who primarily focus on defending.
I'd probably say leadership is their other concern. I like Brady Tkachuk, he's gritty as heck and willing to answer the bell with no hesitation. Does most of his scoring from the toughest areas of the ice. He's clearly the team's emotional leader and I just don't know if he's quite mentally mature yet to handle that. Just often seems to caught up in the bullshit. Not trying to rip the kid, he's still just trying to grow into the role and doesn't have enough veteran support around him. Giroux was probably a big help. Stutzle is another key player who is just still so young, he's going to get so much better in his overall game still. There will always be some risk/reward with a player that highly skilled, but he has to learn to clean up his decision making in certain areas of the ice