Stormforce is an incredibly complicated, old, and prototype or near prototype ride model. It has hundreds of sensors, motors, lifts and moving platforms below or in or just above water level. If any of these are down, the ride cannot operate safely, and therefore will not operate full stop. If any one of the light gate sensors used to track the boats trips erronously, the whole ride will shut down to prevent blocking errors. The ride is more than prone to shutdowns than most other attractions in the park for this reason, and by its very nature, these shutdowns are almost exclusively last minute and unpredictable. The park had no way of knowing the ride would be down excessively that day, and could not predict it. It opens at 12 to give time for these errors to hopefully occur and be remedied before opening, but there is no garauntee. The HSE wrote a very clear set of guidance after the accident on the rapids in 2017, that means that Drayton are rightly very cautious with free flow open water rides. They will always take the decision to close over a faut, no matter how minor, than potentialy have any kind of risk.
TL;DR
The ride is very prone to failures due to its nature, that cause the park to close it for extended periods of time, with little or no warning. This is comletely normal for the ride and other water rides in general, due to high safety standards.
