Relay attenuator plugin doesn't change the volume

I have the relay attenuator plugin V1.3.0 installed and have connected a line input through the attenuator. I can play music through the input and hear it (much attenuated), but I can’t control the volume. Using the UI I have changed the attenuation from 0 all the way to 100; there is absolutely no change in the output level.

This could well be related to the other bugs that I reported, but I don’t have any way to know that. Since the symptoms are different I reported them separately.

I started from scratch with Volumio 2.5.87 and got the relay attenuator plugin to install, apparently successfully - it didn’t give any error messages. However, the attenuator does not work, at all. It does absolutely nothing, no matter where I set the volume. It appears to be set to maximum attenuation - I can hear the music playing very softly, but the volume never changes when I change the setting through the UI. If I bypass the relay attenuator (unplug the cables and plug them into female-female adapters) then I hear the music at normal volume.

So, either the software has some major bugs or I have a defective attenuator; either way, I would like some support. Posting a bug report for a purchased product and not getting even a ‘Gee, we can’t reproduce that’ after a full month is not good customer support.

I am quite competent with the Linux command shell, so if you have some troubleshooting suggestions I would be glad to try them.

I submitted two sets of logs; the first after simply booting the system, and the second after changing the volume several times.

It appears that the relay attenuator is never getting initialized; usually it comes up with both channels at the same volume, but twice it has come up with the right channel quite a bit louder than the left channel.

This looks interesting:
2019-07-28T21:29:36.148Z - info: Volume script /bin/sh /data/plugins/miscellanea/allo_relay_volume_attenuator/ 18
2019-07-28T21:29:37.492Z - info: Cannot set Volume with script: Error: Command failed: /bin/sh /data/plugins/miscellanea/allo_relay_volume_attenuator/ 18
[sudo] password for volumio: Sorry, try again.
[sudo] password for volumio:
sudo: 1 incorrect password attempt

I did change the password after enabling SSH access, but that was only after multiple attempts to get the relay attenuator to work. That is, the attenuator and Volumio were unable to change the volume long before I changed the password.

I reinstalled the OS and the plugin, did not change the root password, and ran the tests again. Still no control over the volume, but no SUDO errors in the logs this time.