What daf** are you on about? He played very well in every match he played. In the last couple of games Mavididi is not tracking back enough making it harder for JJ to defend the same as it was with Barnes and whoever played LB. Haven't you noticed that Mavididi is less tired and more productive lately. It's because JJ does most of the work.
We never really had problem on the LB position, its our left wingers not putting enough effort on defense.