Stars don't tell you the condition of the players.

There are hidden variables in all players that decides performance, thus players have slump periods you'd better bench them during that, no matter the quality, a player getting low rating will undermine the team as a whole.

A particular severe slump can last up to 2 whole seasons, although most are light and it only last for a few days or a week.

ST failing to score may not be directly caused by their own form, but the midfield failing may exhaust them in the defense causing offensive performance to plummet.
If your midfielders are doing well while ST/AM not, bench those.