Hi,
I am not sure whether my post would be of any help to you. I will just add my perspective. Such things are pretty common with practice tests. Please take practice tests only to improve your timing, and to learn from your mistakes and to learn new methods. No test is going to give us an accurate score(the score we feel we deserve). Well, We may think that practice test scores will make us feel more confident but that is one aspect about which we need to rethink. The only way to go forward is not bother much about practice test scores and just review them. I also think Knewton diagnostic(CAT 0) is a bit liberal when it comes to scoring. Anyway, I can't prove this, just from my experience. Getting 6 or 7 incorrect in Verbal means you are doing well. No need to panic.

The scoring depends more on the difficulty level of questions answered incorrectly than the pure number of questions answered incorrectly.

For example, getting a level 700+ question correct will count for MORE than getting a level 300+ question correct. Likewise, getting a level 700+ question incorrect will hurt you LESS than getting a level 300+ question incorrect.

This is my understanding of it anyway, someone please correct me if I'm wrong!