His game at Southampton was to push the defence up and help their pressing game from the back. Thus far it seems like he knows that it is exactly this Brendan wants him to do, but he doesn't have full faith in those around him to do the same. Hence he sometimes over commits, leaving him a yard or two further up than his cohorts, meaning he looks slow or like he dives in.
I don't think tonight, and their goal was a representation of this though. The impressive Marcelino picked up a pocket of space in an inside right position as Moreno was bombing beyond Sterling, which left Ludogrets two on one with Sahko. The ball was neat, Lovren was in a relatively decent position given the situation, it just seemed worse by Mignolet's rush of blood.
He will come good. It's 3 new players of a back 4. It'll take time.