Rare and unheard of bug! Could it be maybe your keyboard? Or are you using a gamepad? Which operational system are you using? Please provide some more information on your platform, and I'll try to help you.
Meanwhile, please try out this official Microsoft keyboard tester, to see how many keys does your keyboard support being pressed at the same time, and if it properly detects the keys that you are pressing to jump + dash at the same time:
https://www.microsoft.com/applied-sciences/projects/anti-ghosting-demo