Hey @kohenkatz, thanks for reaching out! This is actually a limitation of the Z-Wave specifications. When the default volume is set to 0, Z-Wave defines the device as silent and inactive. In that state, the device is not allowed to behave as if it is actively on.
Keeping the LED on or controllable while the volume is set to 0 would make the device report an active state to the hub when it is supposed to be inactive. That violates Z Wave supervision rules and causes certification test failures, which is why this behavior is not allowed.
If the goal is to use the LED without sound, there is an option for that. Parameter 1 set to value 4 disables the speaker and uses the LED only. In this mode, the LED will flash for alerts and the volume setting does not matter, since audio is fully disabled.
Please let us know if you have any questions!