As for the goal against Napoli, he's come wide to fill in for an out of position fullback like all CBs have to do at times. Sometimes they can win the ball or hold up play, sometimes they cant. On this occasion Napoli are able to find a pass again exposing the fullback out of position. The ball comes across the box and Gomez isnt able to get there.
Again this is something all CBs will do. Its not a good look if your defense falls apart when 1 CB has to cover someone else out of position. Smalling will do this often when Valencia is out of position. If the opposition score its not his fault. Varane will do this if Carvajal is out of position. If the opposition score its not his fault, he had to cover for someone else out of position. So no its not VVD's fault that Napoli scored.