From your debug log, it shows you have Apache2 running as a web server and this is interfering with lighttpd (the Pi-Hole web server) on port 80. You will need to either stop Apache2 or move it or lighttpd to an alternate port if you want them to run together.
*** [ DIAGNOSING ]: Pi-hole processes
[✗] lighttpd daemon is failed
[✓] pihole-FTL daemon is active
*** [ DIAGNOSING ]: Dashboard and block page
[✗] Block page X-Header: X-Header does not match or could not be retrieved.
HTTP/1.1 200 OK
Date: Mon, 09 Sep 2019 15:24:20 GMT
Server: Apache/2.4.25 (Raspbian)
Content-Type: text/html;charset=UTF-8
[✗] Web interface X-Header: X-Header does not match or could not be retrieved.
HTTP/1.1 200 OK
Date: Mon, 09 Sep 2019 15:24:20 GMT
Server: Apache/2.4.25 (Raspbian)
Last-Modified: Mon, 25 Feb 2019 13:14:11 GMT
ETag: "2a3b-582b7b765ffd0"
Accept-Ranges: bytes
Content-Length: 10811