Help with arcade stick / pad input accuracy issue



Let me first state that I am a complete novice to a game of this genre and I am having massive trouble when it comes to any key combination that includes diagonal movement of the character.

I used to play this on Dual shock 4 (used analogue key for movements, same problem.) and now on a custum arcade stick I made (Sanwa JLF lever, OBSF 30mm Pushbuttons, Thanks to all the guides in the tech forum!).
And the problem occurs in both input devices.

When I press 236 + A/B/C (once), A/B/C is registered multiple times.

I try to get clean diagonal input, tried 10 times see what I get :

So I find it extremely difficult to do any propler skill shots right now.
I know I need more practice but Is this normal?
The game seem to be too sensitive that I actually find it unable to play.

Any help would be appreciated.

Thank you.