I'm not yet convinced that your issue would be related to Lighttpd failed to start on fresh install - configuration issue, Binog.
wieb's observation evolved from a PHP error over a port conflict with Apache and a lighttpd startup issue (all web UI related) into outright DNS failure due to lack of upstream connectivity.
Does your lighttpd fail to start as well?
Did you see the same PHP error?
Do you also run Apache as webserver, instead of or in addition to lighttpd?
Did you see the same lighttpd error?
Is DNS resolution also failing for you?
Does your Pi-hole run on Armbian as well?
Do you have the same peculiarities in your routing table?