Hi Aidan,
Something we found before rebooting the containers and that we find strange is that the default balena-engine bridge only contained the mqtt container. And name resolution was working from inside that container (via the 127.0.0.2 default resolver), but not from inside other containers.
In comparison, after rebooting the containers all of them are part of the default network.
So what we are looking for is the cause for containers to leave the default bridge.
We will discuss internally to try and hypothesize something and come back to you.