This happens to me. It aways happens when I am a few points in front at the top of the Premier.
3 or 4 up at half time, then I'm lucky to scrape through with a draw, all my important player ratings go down to 6, when I sub them other players go down to 6.
Then after a few games I am a few points behind in the league and everything returns to normal.
I know people keep saying nothing is scripted, and I believe them, it does make me wonder sometimes.
SI's AI gone mad perhaps?