Ubuntu 16.04 (intermittent) and Debian 10 (every time for @deldesir) are not the only ones.

On some distros it happens every time, whereas on others it's intermittent ("./iiab-install --reinstall" can sometimes work to overcome this failure in 4-server-options).

In all cases, iiab-install fails here in Stage 4 (4-server-options) when dnsmasq fails to start:
https://github.com/iiab/iiab/blob/master/roles/captive-portal/tasks/main.yml#L141-L145

Sometimes ./iiab-network ("./runrole network") fails in apparently the same way — with dnsmasq strangely unable to start. Confoundingly, "systemctl start dnsmasq" seems to run fine [certainly on Ubuntu 16.04] when run manually at the command-line !

Thank you @deldesir @jvonau @georgejhunt for continuing to monitor this pattern towards identifying the root cause — so we can put an end to this in coming weeks if not days!

Refs: #1182 #1364 #1387 and others

Possibly Unrelated: @jvonau asks if 127.0.0.53 in Ubuntu 18.04's /etc/resolv.conf has anything to do with this? https://github.com/iiab/iiab/blob/master/roles/sugarizer/tasks/main.yml#L181-L182