Reached 700 Level questions in Prep Verbal but crashed at 27

Hello everyone,

I am to take the real GMAT next Wednesday and I am a bit disturbed by the Prep I took today.

I started my GMAT preparation 3 months ago and at this time scored very low in verbal (23 and 25). I followed rigorously MGMAT books and improved my verbal scores reaching 38 twice under the MGMAT CAT tests. I then thought I improved the Verbal section but my Prep score returned 27 today!

I'm very confused because while I made mistakes, I faced 700 level questions such as my #29 ("When drafting the Declaration of Sentiments that was adopted..."). I wonder how could my score dropped that much?

Some other information on my verbal part:
- 1st question wrong on SC
- 2 wrong answers (including #1 SC) in the first 11 questions
- 3 hard SC questions answered incorrectly in a row (#12, 13, 14)
- Did Ok up to question #29 where I faced the question mentioned above
- 4 questions answered incorrectly after #29
- By the way, I scored a stable 45 in Q and ended up with a 600

I'll focus my last hours of preparation on SCs but I'm still looking for answers on the reason why I crashed that badly.

Thanks for your help

Florent