Hi,

Yes, fluctuations in practice test scores are normal and to be expected. There are many reasons for this, including:

-as you learn new strategies and approaches to problems, you may slow down initially until you master these approaches, causing a dip in your scores at some point, which then recover later on
-you may learn or re-learn more of the content you've forgotten at various points in your studies, influencing your scores
-your time management and concentration may fluctuate depending upon the setting and circumstances under which you take the tests
-even the real GMAT has a 30 point margin of error, so fluctuations on different days are to be expected

The good news is, on an adaptive test, theoretically you cannot score higher than your actual ability level, because if you guess correctly, you then get a harder question, and if it was just luck, you would probably get the harder question wrong. So your highest score is representative of what you are capable of, the lower ones are potentially bad days (note: that is part of the reason why MBA programs tend to take your highest GMAT score as the one they look at for admissions). So it looks like you are certainly capable of scoring over 700 which is great, just make sure you finish up your studies, focus on the areas you are still weak on or the questions you got incorrect on your CATs, and stay calm, confident, and focused on test day. Good luck!