Its still a fairly new ride and very new technology. Most of the time, everything works but like anything, sometimes it doesn't. I believe they are still working everything out.
As previously being a bigger person, I cannot understand why people continue to not try the test seats and then complain about the ride. Seriously???
The test seats are there for a reason. Try them. If you don't fit or you are not comfortable - do NOT ride. There are about a million warnings for Gringott's not to ride with these conditions, etc. Obviously poster who complained a bunch earlier in thread, ignored all of that. If he was in the crazy amounts of pain, he would have said something immediately or at least by that first turn stopping area. You are there for at least a minute or two. If I was in pain, I would be waving my arms like I am trying to land an airplane to get attention.