I'm sorry you had such a disappointing drop.
The good news is that I can think of several (good) reasons why this might have happened. The bad news is that there are also some not-good reasons why.
So we need to figure out why your score dropped.
It looks like the score jump on test 3 and the score drop on test 4 can mostly be attributed to quant, so we'll concentrate on that section.
First, did you take both tests under identical conditions? Did you do the essay and IR sections on both? Did you take two 8-minute breaks at the appropriate time? Did you NOT use the pause button? Etc.
Second, are there any outside reasons why you might have been objectively burned out / wiped out before you took the fourth test? Did you take it after a long day at work or after studying for 6 hours straight?
Third, what was going on with your timing? This is the
single biggest culprit of score drops.
What happens a lot: people learn a ton, feel really good, take a test, get stubborn because they feel like they "should" know how to do something, mess up their timing, and blow the section. Could this have happened to you?
Use this article to analyze your last two tests (you can just do quant for now and then do verbal later).
http://www.manhattangmat.com/blog/index ... ice-tests/Pay extra close attention to timing issues. In particular, look for situations in which you were spending a lot of extra time (above about 2m45s) on certain problems and then rushing on others to make up for it. How many of those too-long problems did you get right in the end? And how many rushed problems did you miss due to careless mistakes?
If this is what happened, that's a "better" reason to have a score drop - because you want to do that in practice, not on the real test. You need to fix your mindset - which isn't easy, but it's easier than the next scenario, below. Use these articles to help you get started on that.
https://www.manhattangmat.com/blog/inde ... lly-tests/http://www.manhattangmat.com/blog/index ... -the-gmat/Alternatively, a lot of people won't do the essay and IR sections at first because they're concentrating on Q and V. Then, when they finally start to add in the earlier sections, they have a big score drop on Q, V, or both. This is a "bad" reason to have a score drop because it's probably going to take longer to fix. You have to learn how to maintain mental performance over the length of a 3h40m test instead of a 2h30m test. That's a big difference.
Use the above to help you figure out what you think is going on. Then come back here and tell us. Also tell us what you think you should do about it. (Part of getting better is developing your ability to analyze your results - figure out what they mean and what you think you should do about them!)
Then we'll tell you where we agree and disagree, and we'll advise you further.