Got the same problem and a very similar setup, innous mini and devialet 220.
Here is what I have tried
1] both the innous and the devialet is connected to the router
then I both see a no-connection, like the one you describe,
and also loss of sound. But only the sound, the music keeps playing.
The sound comes back after 10 - 20 sec
2] if I add an usb cable between innous and the devialet, and setup roon to play
via the USB, then I only see the lost of connection
3] starts playing music using setup described in 2] and
then disconnects the Internet cable between innous and the router,
then there is no problem at all [ well of course apart from, that I have to connect the innous again
if I want play something else]