What is Form Score and how does one maintain it?

Form score is strictly based on point production, mostly goals. If you get a goal, you are pretty much guaranteed a form score greater than 80, unless you give up a bunch of goals.

otherwise, the simple answer is this was a task probably relegated to an intern over at EA sports and then was not QA tested by any user (unless they played on rookie). 
I recommend you stop playing the game until they fix this.