Thanks :) the inability to jump on your own once fully grounded was a core design choice to satisfy the "don't stop" theme, in this case don't stop jumping with the right timing. You can get bouncing again if you fall down to a lower level and time the jump button as you land. A lot of the level design is full of steps so you can have multiple opportunities to try to recover.
Whether or not that's a good design choice, though, that's another question 😛
A few things I think the game really needs slipped through the cracks as I ended up losing a lot of time to various problems. Some sort of feedback when reaching a new checkpoint and a small into cutscene I had planned would've both made the goal direction clearer I think.