Keep in mind that year after year the Packers are among the youngest teams in the NFL. Perhaps that has something to do with tackling? I mean, you can teach tackling fundamentals all you want but it's not one offseason of work to improve a guy's tackling. Veteran players are naturally going to be better tacklers; more time to practice it and the fact that poor tacklers won't last long. However, this year's Packers team is the third youngest in the NFL. The defense is fielding Hayward, three years in but one of those years was a waste, a rookie corner, a second year safety, a second year ILB and third year DE in Jones (this is when the team is at full strength).
According to PFF the Packers missed seven tackles against the Bears. Two by Clinton-Dix, two by Shields and one each by Jayrone Elliott, Nick Perry and Hayward. It's also worth pointing out that Clinton-Dix and Shields lead the team (along with Matthews) with six tackles (again, PFF numbers). I'm not going to get to bent out of shape when a couple second year players have a few missed tackles in a game where the front seven was doing a terrible job of stopping the run and forcing secondary players to tackle running backs.