We've looked into it and we think the problem is that some might not see the fuel bar for sprinting for it being too small and unnoticeable because the arrow keys and wasd both work fine with spacebar
strange , i was well aware of the fuel bar and had it full when attempting the jump but at least 10 times out of 10 it literally would not jump when using the up arrow key and then when i switched to wasd it worked first time, and a few times after that - i switched back to arrows and again couldnt get it to work so i assumed it was a problem with the keys ?
just checked again and still not working for me !