I am having this problem and have rebooted and shut down/restart all devices multiple times without success.
Previously I used a Windows 10 machine as the Roon server and connected to my DAC (Moon 380D) and was able to control the volume from my preamp, Windows 10, the Moon unit, and from the Roon app. Now I can only control volume from the preamp.
The problem started when I installed the ROCK on an Intel NUC. I used the exact hardware recommended for the ROCK (NUC10i7FNH plus recommended RAM and M.2 SSD). I also updated the bios and installed ffmpeg. ROCK was also updated to 1.8 during the installation process.
Now the server and all of my controllers are on the new version. And now I can only control volume from my preamp. Please help.