auto lo
iface lo inet loopback

Anything else, and in particular any lines mentioning wlan0 may well confuse the situation.

When I installed Devuan ASCII, I configured my wireless network using the expert installer. While NetworkManger does connect, I have no actual Internet connection (can't ping).

I have to issue the following command to actually get it to work:

$ sudo dhclient wlan0

Only then /etc/resolv.conf is populated.

It's only a minor annoyance but I'd like to know how Devuan actually configures the network during installation so I can properly fix this.

I'd prefer to keep using NetworkManager rather than setting managing the network via /etc/network/interfaces (which apart from the loopback device has no entries).

Note that my system has network-manager 1.6.2 installed.

Thanks!