Mount jumping bug
I noticed the jump uses the endurance gauge, was it empty when you tried? My mount will not jump if the gauge is empty.
You can allow your mount to jump without using endurance if you check the “Disable Conditional Mount Movement Ability Input” box at the bottom of the Options menu (first options tab, scroll aaaaaaaall the way down). After that, your mount will merely do a standard jump when you hit spacebar, and will only do the conditional mount movement ability (e.g., for Raptor, the long-jump) when you hit the keybind you set for it (default is V, iirc). Running out of endurance might’ve been your problem, although I somewhat doubt it. But, hey: just in case.