Thank you so much for playing my game, and for making a video of it no less!
The disorienting nature of the collapsing platforms seems to be a big issue with the game, because it's hard to tell if you're falling when you are moving with the platform.
About the water-based double jump, it's supposed to happen whenever you press space mid-air while the "emergency double jump activated" text is displayed (the double jump activates whenever you touch water). It seems as though some kind of bug may have occurred there, but it is hard to tell because it seems to work as intended on my end.
I think at some point you mentioned collapsing a region on purpose, and that is actually how you get into the "water caves" in the bottom-left (the enclosed set of regions that you couldn't get into)!
Again, thank you for playing my game! After the jam ends, I may do an update where I add more background elements to make the falling platforms less disorienting, and maybe add a hint that you can collapse regions on purpose. I might also add a way to read the tutorial without restarting the game :P