Ok so the current Montu downtime is unrelated, but I can give a brief description of what I know, which isn't too much.
Cobra's Curse somehow rolled back to a certain extent, which likely led to a valley and/or collision- not entirely sure. Since then, it has reopened with some change to the lift hill that makes it louder.
Montu, on the other hand, I am not entirely sure about. It supposedly valleyed after losing some part (unsure of what), or something to that extent the other day, and was then closed immediately.
And not that you asked, but Tigris is likely down to remove the Comfort Collars, as are Tempesto and Electric Eel at the moment.