From your debug log most things seem to work, only a few are a bit suspicious/uncommon:
There is not DHCP server on your network?
*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
Scanning all your interfaces for DHCP servers
Timeout: 10 seconds
DHCP packets received on interface wlan0: 0
DHCP packets received on interface lo: 0
There are a few restarts of the web server (lighttpd). Did you manually restart it?
2021-02-22 09:31:35: (server.c.1464) server started (lighttpd/1.4.53)
2021-02-22 09:36:33: (server.c.2059) server stopped by UID = 0 PID = 1
2021-02-22 09:36:35: (server.c.1464) server started (lighttpd/1.4.53)
2021-02-23 07:49:06: (server.c.2059) server stopped by UID = 0 PID = 1
2021-02-23 07:49:07: (server.c.1464) server started (lighttpd/1.4.53)
2021-02-23 07:45:45: (server.c.1464) server started (lighttpd/1.4.53)
Pi-hole is/has been working
[2021-02-23 08:03:54.951 890M] -> Total DNS queries: 1322
[2021-02-23 08:03:54.952 890M] -> Cached DNS queries: 293
[2021-02-23 08:03:54.952 890M] -> Forwarded DNS queries: 926
[2021-02-23 08:03:54.952 890M] -> Blocked DNS queries: 98
[2021-02-23 08:03:54.952 890M] -> Unknown DNS queries: 1
[2021-02-23 08:03:54.952 890M] -> Unique domains: 471
[2021-02-23 08:03:54.953 890M] -> Unique clients: 14
[2021-02-23 08:03:54.953 890M] -> Known forward destinations: 4
One of your upstream DNS server is refusing some requests. Might be worth considering picking another upstream server
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.220.220
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.222.222
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.220.220
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.222.222
Feb 23 07:56:25 dnsmasq[15129]: reply error is REFUSED
Feb 23 07:56:25 dnsmasq[15129]: query[type=65] star.c10r.facebook.com from 192.168.0.150
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.220.220
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.222.222
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.220.220
Feb 23 07:56:25 dnsmasq[15129]: forwarded star.c10r.facebook.com to 208.67.222.222
Feb 23 07:56:25 dnsmasq[15129]: reply error is REFUSED
Feb 23 07:56:28 dnsmasq[15129]: query[type=65] me.apple-dns.net from 192.168.0.157
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.220.220
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.222.222
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.220.220
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.222.222
Feb 23 07:56:28 dnsmasq[15129]: query[AAAA] me.apple-dns.net from 192.168.0.157
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.220.220
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.222.222
Feb 23 07:56:28 dnsmasq[15129]: forwarded me.apple-dns.net to 208.67.220.220
Regarding the non-working index:
Did you try to clear your browser's cache? Have you tried with different browsers? Are there any errors shown? Do you have any browser plugins installed?