The Menu Doesn't Open On ESC#
Cause: the hook is off, or something else is intercepting the key.
Solution: try /pausemenu first. It opens the same menu without the hook, so it tells you in one keystroke whether the problem is the menu or only its trigger.
If /pausemenu works, check Config.Menu.replacePauseMenu.
I See GTA's Menu For A Split Second#
Cause: this is inherent to the approach, not a bug.
Solution: nothing to fix. Escape does not travel through FiveM's control system — the frontend opens the pause menu itself, so watching for it and dismissing it is the only reading that works. That costs one frame.