Here’s the response from Simaudio support:
Thanks for reporting the issue.
There have been a number of reports of similar issues following firmware updates to the MiND module. When Roon has control of the MiND, which then resets itself without resetting the whole 390, Roon may lose control of the preamp. Luckily, the fix is usually simple: power down the 390 using the rear rocker switch or by disconnecting the power cable for about a minute. When you power it back on, Roon should re-establish its control over the MiND and the preamp. If not, then rebooting the Roon Core usually does the trick.
However, you indicate that you’ve already followed these steps unsuccessfully, and that is extremely rare. So then please use the on-screen Setup menu on the 390 to Reset the unit to its factory default settings. You’ll have to rename and reconfigure the 390 and its inputs, and re-enter the Wi-Fi credentials if it’s pertinent. Then Roon should allow you to set up the 390 like a new device. After that, if there’s still no control of the preamp, there must be an issue somewhere earlier in the chain.
Please let us know if that helps.
Unfortunately I tried their recommendation and it still did not resolve my issue. I then did a clean install of Roon on my IMac and went through the power off cycle with the Moon 390 and the problem still exists. I still cannot get control of the volume on my Moon 390 using the Roon Remote app on my IPAD which is something I used to be able to do up until a few weeks ago.