itch.io

You are not required to hold the space bar, here is proof:

I created a macro that holds the spacebar for exactly 1 millisecond: https://i.imgur.com/k1Lxbl2.png
And I tested it in game with a keyboard visualizer: 

The problem may lie in your inputs going missing, which may be caused by multiple factors: Low framerate, malfunctioning keyboard, not enough RAM or other factors.