There is a problem: it is impossible to press more than 6 buttons at the same time. Most likely, this is related to the length of the array that stores what is currently activated. The length of this array is 6 elements as buttons on linked
controller and possibly increasing this length to 25 (the number of buttons on your controller) the problem will disappear.

P.S. translated by Google translator

Is there anything new about your problem ?

This part of the code does not use an array (in opposition to create's linked controller implementation, which does uses an array). Instead, I use a 16 bit bitmask to send the state of all buttons, and another 32 bit variable to store the analog axis values. Here is the relevant code: ControllerRedstoneOutput
I tested in a world just in case, I can press simultaneously all buttons of the controller without any issues.

What are you using as input source, a keyboard/mouse or a gamepad ?
If you are using a keyboard, then I think the issue is that your keyboard can't register more that 6 keys being pressed at the same time. In this case there is nothing that I can do since its a hardware issue.
You can check this using the following website : https://www.mechanical-keyboard.org/key-rollover-test/

Closing this for now, let me know when you have anything new on this and I will reopen it