Surely the easiest solution to this would be redesigning the outerbank so it's a bit lower? Obviously easier said than done, but I don't really see any other way to solve this stalling issue. Unless a wheel change would do it, but surely they would have done that by now?
I know it's only happened when empty so far, but surely Merlin aren't going to want to run the risk of it stalling with riders on (if only to avoid the press headlines...)?
I still haven't ridden yet, as it has felt like too much of a gamble so far, as I live 3.5 hours away, and don't want to make the journey for it to then be closed
there are many ways to reduce the drag on the train, redesigning the ride would require new support structure, new track, a lot of work, and it could be extremely difficult, rollercoasters (in fact most buildings) are designed to be built one way, I can't recall how hyperia was built, but there will have to be a full assessment on how to disassemble the track, then reassemble it without causing potential structural problems.
the ways you can reduce drag are many:
wheel compound: similar to F1 rollercoasters have differnt compounds from cold wether (harder, less rolling resistance to combat the more thicker cold grease) to hot (softer, but able to withstand the hotter temperatures)
wheels compressment: there are adjustments on the train to adjust how much the wheels are pressing into the track, if to tight it will introduce too much drag.
the wheel grease being used,
and so much more
you also have to remember a lot of stuff is wearing in at the start of the season, after a bit of running it will naturally reduce its drag and it is a new ride, it has only vallied what 3 times now, the second time they got it back running very quickly if I recall correctly, they will be working out new operating procedures to prevent this, valleying isn't a new issue with hyperia, the smiler struggled with it and it is primarily based on the layout of the track.
