Volume level reverts to full upon reboot.

I am using MacOS Mojave 10.14.6 on a mac mini 2012. Every time I reboot my mac mini or it restarts due to power failure the volume level reverts to full. If I reboot the device the volume level remains the same, but if I shut it down, switch the power off ( unplug the power cable) the volume level reverts to full. I turned off the internet connection and the auto-update of time to off. After that set the time a few years back and shut it down then removed the power for a few minutes, seems like the time holds. How do I fix that?