Alright everyone, and especially the developers, if anyone is having trouble performing the Hadouken, I found the issue in my case.
It turned out to be controller. I’m using a PS4 controller, which is normally supported by the game. However, when I use the controller, I simply cannot perform the Hadouken at all(managed to get it to work once, but after that, I couldn't get it to work again.).
But when I disconnect the controller and try using the keyboard, the Hadouken works every single time.
So I tried hiding the controller from the game and using JoyToKey to convert the controller inputs into keyboard inputs instead.
And now the Hadouken works every single time.
Also, it seems like this method fixes the issue where controller inputs delay at some moments. The only downside is that the controller's vibration function won't work.