I don't know enough about the coaches, how they operate day to day, what they're asking the players to do, etc to answer that. If you're going off pure on field performance, the biggest positions that worry me would be LB & OL.
OL is young with some square pegs, so i think that will get better but will just take time. The LB play deeply concerns me, and if we're seeing the same things in 2 years, Frost will have to make a move on his defensive staff.