Probably, the questions you saw on the three tests were from different areas you are strong in.
Another reason could be that you are expecting perfect results on GMATPrep because you know inside that it mocks the tests more than other prep companies.
(I am doing critical reasoning here
Review your tests to see why you got those scores. Check each wrong answer and weak area. You will probably get an idea why yout got those results. But important thing is to learn from your mistakes.
All d best.












