So we have from witness accounts:
- ride was going too fast
- ride was going too low
- seats were shaking
- operator was fiddling with the controls, apparently unsuccessful to remedy whatever was going wrong
which led to
- two people (at least) being thrown out of their seats and harnesses (were these old harnesses that had not been replaced, similar to the water slide accident a while ago?)
- a row of four seats completely breaking out of the ride
It looks to me that possibly there were several factors coming together (as often is the case with such tragedies):
- the ride was not operating correctly, going too fast
- the operator was not able to do anything about it in time (possibly human error)
- the equipment (seat and harnesses) came apart due to either improper installation or fatigue, plus the stress of the increased speed.