Taking a look at the forwards since Sutter took over, it is incredible how much Monahan has struggled.
According to
this forwards shot attempt table, Monahan is dead last in shot attempt % among forwards (14/14) and is the only forward on the team that is under the 50%.
Combine that with only 8 points (6EV, 2PP) in 20 games and it's clear there is a problem. It's not icetime, since he's been getting more even strength icetime than Lindholm, who is producing. The problem may be Brett Ritchie, who is not good and whose on ice goals for % is 23% (which is incredibly bad and about 18% lower than anyone on the team not named Monahan [35.7%]).
It's hard to find anything really positive to say. Monahan has fallen off a cliff and there does not seem to be an effort issue, so other than moving him at an all time low value-wise, I don't know what they can really do other than keep him away from Johnny.