The test was still adapting as you went. :)
Multiple possibilities. First, the database is allowed to choose from a broader range of levels than you might think because it also has to balance various other parameters - a certain # of PS vs DS, a certain number of geometry overall, a certain number of triangle vs. circle Qs, etc. It's not only about the difficulty level.
Second, the data that you're seeing in the report is not necessarily 100% accurate / what's in the database. When we first post a question, we assign a difficulty level to our best-guess estimate. As people do the questions, we track the data and assign a real difficulty level based on actual results. The database difficulty values then get updated, but the field that shows you the difficulty range has to be manually changed in a completely different way and by a different team than is handling the assignment of the real difficulty values - so there is always lag there in updating the "viewed" difficulty levels vs. the real, new levels assigned. You could have had a few of those.
Finally, the database is not allowed to choose questions that you've seen before (in the same set of 6 tests), so that limits the options as you take more tests, particularly if your scores aren't changing that much. (I'm guessing this isn't what happened in your case, though, because usually the consequence here is that someone "uses up" the 700+ question pool by scoring very well from the very first test, and so they drop to 600-700 sooner than expected - but that's not what happened to you. I'm just including this possibility for others reading this.)
Now, let's talk about the more important issue: what are you doing about that timing problem?
Read these and start doing what they say! :)
http://www.manhattangmat.com/blog/index ... to-win-it/http://www.manhattangmat.com/blog/index ... nt-part-1/