One of a couple of things might be going on. (Also: to the guest's post about your score being "already narrowed down" after 15-20 questions - that's not how the test works. You could do a great job on the first 15-20 and do a bad job on the rest and your score could tank. It's a myth that the earlier questions "set" your score and then it won't go down.)
First, how many practice tests have you taken and how were you scoring in quant on those? If you were scoring very high in general (that is, using up a lot of the 700-800 questions) and you've taken 4 or more tests, then you might have used up most of the 700+ questions. The algorithm isn't permitted to give you questions you've already seen until test 7, so it will give you lower level questions but still keep your score high b/c it knows it's giving you lower level questions simply because you've used the higher ones up for the most part. This obviously won't happen on the real test - it's a limitation on practice tests specifically if you're scoring at a high level on many tests.
That's the most likely scenario, but if you haven't been scoring very well on enough tests that you used up most of the questions, then it could have something to do with the fact that you got disconnected. I've seen that happen once before with another student - after the disconnect, something got messed up with the algorithm. But I've only heard of that happening once!
If you think it might have been the latter scenario, send an email to
techsupport@manhattangmat.com and ask them to take a look and see if something went screwy.