Confidence is shot. Dembele had similar phases. One already earlier this season after losing his starting spot before big daddy Vidal set him straight.
Coutinho was shit to pieces a few weeks back.
It is the Valverde way
Dembele responded to bad stretches and being benched by doing superb work as a sub, getting back into the starting lineup. Coutinho is not having a great year, but still perks up with man of the match type of performances sometimes. Vidal was completely out of favor, earned his way back into the starting lineup, now is out again, he will be back.
I've heard way too many excuses for Malcom. Most players who join this team prove they need to leave within the first year or two, I see no reason to expect him to continue long in this squad.