So when I heard about this I was not really surprised that this happened given all the trouble the ride had in the beginning. However looking at the pictures I have come to suspect that one of two scenarios likely played out here:
1. The guest left the boat causing the guest to strike the catch net.
2. The boat left the slide with the guest strapped in and that caused the guests to strike the catch net.
There are currently conflicting statements from eyewitnesses over the seating arrangement of the deceased and whether or not another guest seated in the unit was injured. If multiple guests are injured the later is more likely than the former based on the restraint design. I imagine that in the later scenario a weight imbalance and maybe an overspeed or combination or flow off the water jets caused the back of the boat to rise up. Put all the weight in the front of the boat and its not that hard to flip it. Not only have I seen it happen, but I have experienced it first hand as a kid. When I was 11 me and my dad went down a waterslide in a double tube. He weighed 250lbs and I weighed 50lbs. They made him sit in the front, the first quick dip we went down I got thrown into the top of the tube and rolled out into the runout section dazed and confused with a terrible headache.
I think everyone remembers the video that was released showing the units on this ride under the original design gaining flight like some twisted Roller Coaster Tycoon contraption. If memory serves me correctly they made some profile changes and redesigned the back half of the ride. That wasn't enough so they added friction materials to control the speed these are seen at the bottom of the first drop. The opening day videos and some videos I found from 2015 seem to indicate a guide in the trough on the first drop was installed and it seems to slow the boat down. That trough is removed in the 2016 videos.
Reviewing the available videos of the ride I also noticed that there was a change in the water flow from the original 2014 video to the 2016 video that was taken four weeks ago. Without a bunch of video data taken from them and now it would be impossible to figure out if the average speed is higher then it was in 2014. However it could be duplicated if the original conditions were restored. The park hasn't really announced anything, it's very early in the investigation, and this is my opinion as to what happened.