There are so many factors, it's quite difficult to advise, to be honest. From a quick glance, the only player that stood out to me was Food, but I have no way of knowing what formation/tactics/level of opposition you had or were playing against.

DMC's & MC's are notorious for bad ratings. I've had a MC score 2 goals, get an assist, block several opposition shots and still get a 5.
GK's are often harshly done by in the ratings, also, in my experience.

If you have players that you only play against the poorer teams in your league, and their form looks good, it could be misleading. Conversely, if your best players are always playing against the best teams, it could swing the other way.

My personal opinion is that I will suffer the odd 5 rating as par for the course, and even the odd 4, but a string of 4's is unacceptable. I've had a 3 once, and I sold him instantly, but never seen lower than that, except a 0 in the case of an early injury/red card.

If I find a player never gets above a 6 after 15 games, I sell them, even if they are 7-star. I would rather have a 5-star performer than a 7-star dud.

But that's just me.