"Mysterious" volume issues

I’ve 2 Rasperry Pi 3 both with Hifiberry Digi+ hats, one of them is connected to a Parasound Pre-Amp on the COAX-input (RoPieeeXL 2024.03 (1450)). The other one is connected via an optical connection to a Marantz CR-6312 receiver (RoPieeeXL 2024.03 (1450)).
The Parasound one is configured as “Device Volume” and the volume can be changed by the (remote) volume control from the device without any problem. However, the Marantz one is also configured as “Device Volume” but I’m not able to the change the volume by the (remote) volume control of the device anymore! For any reason it’s fixed on a certain volume level (but I’m not able to change it, and I’m not aware of which level it’s fixed on). I’m only able to control the volume when I set the Roon-App to DSP-Volume, but then only by the Roon-App, and within certain limits!
Once this was working…
How can I fix this?

Solved by factor reset of Marantz