Jump works for everything (pressing one arrow, two arrows, one numpad key, two numpad keys), but not when you press left + down arrow simultaneously. Pressing “1” or “4” + “2” works.
This is likely an issue with your keyboard.
Some keyboards have keys sharing the same circuit and this cause the signals to not be registered properly. It can vary from one key getting priority or no output at all, depending on the keyboard and how many keys were pressed.