For me it's the quality of the passes. These players have been allowed to develop too many bad habits that are going to be hard to break. Too many players playing at their own pace and not allowing a tempo for the team to build up.
High, slow, bobbly hard to control and a lot of the time played to wrong player, behind the player or to the wrong foot is what we see in passing. When you have to take more than one touch to bring the ball under the opportunity to move it quickly is gone. When you receive the ball to the wrong foot, the chance to get going in the right direction or play it off in one touch is gone.
These players need to learn how to weight a pass and zip it into feet, one or two touches, quick movement. What we see is four or five touches and barely any movement. It's slow and affords the opposition too much time to settle into a shape that is harder to break down. It slows the team down and ypu just see players standing around because they don't have space to run into or they don't know where to make a run.
All in all, it's poor quality passing combined with being slow at moving the ball and a real lack of movement off the ball. It's going to be hard for RR to get that into some of these players, so he needs to get some players into the side who can do it.