6 stars, 7 stars or even 8, they all have bad days i suppose
Give him a day rest (on bench), then put him back on starting line-up, let's see if this works.
About me, i keep using a 4 star (not even close to 5) AML, and he scores a lot.
Recommended players, or scout, they are just like normal player you buy on market, there is no special hidden bonus on those token cost players to expect them to perform better than others.

And what do you expect on a DC? DC usually have low rating even when ur team gets positive results. ST? Hmm i hope u read the threads around here talking about the dropping effectiveness of STs lately. I think u should buy AmL/AMR, or MC on token because they have more impacts on matches.
That's all my thoughts, may be wrong, you dont have to take it seriously