From what I can tell, I've found a fix for the freezing. Just need to change 2 values in the Script.js file.

From Wallpaper Engine > right click Better Matrix Codefall > Open In Explorer.
Find the Script.js > right click > Edit. (It should open Notepad, if not choose Open With)

Scroll down and find "build(row = 20) {" then modify the line below -
From-
if (Math.random() < .3) {
To-
if (Math.random() < .001) {

A little further down find "drop() {" then modify the line below -
From-
color: hsl(`+wpsettings.hslColor+`, 100%, ${65 / len * (i + 0.8)}%)
To-
color: hsl(`+wpsettings.hslColor+`, 100%, ${65 / len * (i + 1)}%)

You will then need to refresh it. Go back to Wallpaper Engine, choose another background, then back to Better Matrix Codefall.

Why is keeping stop for running ? Just stuck after 1 min or so.

It doesn't even move!