StopThePed uses its own flashlight, so try and set Ambient.DisablePlayerFlashlightOverride in the lspdfr.ini to true
When you edited the StopThePed.ini did you edit anything related to
[RealisticWeaponSystem], which is found in the StopThePed.ini
Have you installed any weapon, weapon attachment, or weapon sounds mods?
Next, try to renaming your mods folder in your GTAV root to _mods and then see if the issue persists. This way we can more accurately pin down where the issue stems from