I have the same problem, when the internet goes down I see exactly the same messages and behavior.
I run ROCK on a NUC8i5 and use various laptops, android tablets and phone for control. End points are Rpi running Ropieee. My very basic understanding is that if the core cannot “phone home” it goes off line. In my case I use a samba share on Rock to store my library, when the core is offline I cannot access the library from my internal network,
I discovered this today during two internet outages (rare here) that were not accompanied by a power failure, and at a time when I would normally be using Roon.