I had a problem where my FreedomBox disappears from the router each time the network is disconnected and reconnected.
Whenever there is a power outage of a few minutes (which might happen like once in a week at my place), the router is switched off but the Pioneer edition FreedomBox keeps running on battery power. Once the power comes back on, I found that the FreedomBox does not acquire an IP address from the router. A reboot of the FreedomBox device seems to fix this problem temporarily. I also tried rebooting the router but that has no effect.
I connected a monitor and keyboard to the FreedomBox device and found that the device eth0 has no carrier. I tried restarting the services networking and NetworkManager but that did not fix the problem.
I checked if it’s a broken upgrade by running sudo apt -f install. The package installation of freedombox 19.14~bpo10+1 was broken. I fixed it by running sudo dpkg --configure -a as prompted and rebooted the machine. I think the problem is solved for now.