From your debug log:
*** [ DIAGNOSING ]: Pi-hole processes
[ā] lighttpd daemon is failed
Check this thread for a potential solution: I can't get Pi-hole to work [Ubuntu 18.04] - #10 by RamSet
Also noted in the debug log - the gravity list is empty. Rebuild gravity with pihole -g from the command line.
*** [ DIAGNOSING ]: Gravity list
-----head of gravity.list------
-----tail of gravity.list------