I think it's a combination of problems. Every side we play in Serie A apart from a couple sit back and defend for 90 minutes, and their organization is usually good. With all due to respect to Lithuania, clearly if they played in Serie A they would probably be relegated pretty quickly. Another factor is probably our uncanny ability to play boring, lethargic football, which is part of our DNA. It doesn't seem like it would be a lot of fun playing for Juventus, where the majority of its recent history has been based on a tactical game and where conceding a goal is considered sacrilege. So clearly it's not an easy club to play for, for multiple reasons.
But it's quite obvious Ronaldo hasn't looked great recently. He's looked lethargic and out of sorts, not taking chances as he usually does. If he says he's 100% fit, then he's fit. But he definitely doesn't seem like he's in form, regardless of a hattrick against Lithuania at home. Not really sure what else Sarri can do; it's not like he's making Ronaldo track back to defend all the time. Ipso facto, he's just not playing well and needs to figure it out.