Thanks for trying the demo. :)
I've made multiple improvements to the ledge grab since the demo was released, so this has most likely been fixed.
Here are some of the changed things:
Added a setting that causes left/right to not let go off ledge grab. (on by default)
Added another setting that allows you to aim up/down with the d-pad while ledge grabbing. (off by default)
Added a momentum boost to ledge grab jumping, allowing you to jump further.
So hopefully this fixes the ledge grab issues.
None of this is in the current demo (I think) but they will be the next time I update it, whenever that is.
Anyway, thanks for the feedback, glad you like the game. :)