I don't want to be the "I know something but can't say" guy, but from what I'm aware, the closure after the first day was not to do with the sprocket on the lift hill. I can't say any more than that (because frankly I know very little beyond that), but I think it's important to put that out there so we don't make incorrect assumptions.
As for the latest closure. Firstly, one can't help but laugh. Because if you don't, you'll cry.
Secondly, it's a difficult position Thorpe find themselves in now. Following the original testing and ride opening, the outerbank dive wasn't a particular cause for concern for stalling. But since reopening, it was certainly a concern and seemingly a case of "when, not if". So putting 2 and 2 together (albeit at the risk of getting 5), it's possible that whatever tweaks the park had to make during that first closure, has affected the speed it takes that element during initial tests / empty circuits. Which could mean they have to make further tweaks to stop the initial issue becoming an issue again
and make sure the risk of stalling decreases.
So what do Thorpe do? Do they keep going and have to paper over the proverbial cracks until closed season (not saying they will have to, everything might be fine after reopening again)? Or do they do a prolonged closure now and work with Mack to sort out all the issues? Or something else?
Also, whilst this is highly inconvenient (and definitely outside the remit of "teething issues"), it should be remembered that coasters can and do stall. And many have bad opening years too. But after that, they become fine and reliable.
Just to examples from Thorpe alone:
-Inferno spent about a month of its opening season shut with a train atop its lift hill
-Colossus has stalled on its final turn
-Saw has valleyed at the bottom of its initial drop, and also stalled on the overbank turn following the Immelmann
-Stealth has stalled atop the Top Hat
That's not to say its normal or right or anything, of course. But these things can happen. But just because they do happen, it doesn't mean there's an overarching problem. It could just be needing a different set of wheels. Or warming wheels up. Or just a new machine not wanting to play ball.
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Also, here's a longer video of the rollback: