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If you are Experiencing issues with a Pi-hole install that has non-standard elements (e.g you are using nginx instead of lighttpd, or there is some other aspect of your install that is customised) - please use the Community Help category.
Expected Behaviour:
RPi 3B+ with Buster.
Followed all steps as per setup and pi hole ino DHCP server but still no blocking
Your debug log shows your Pi-hole as operational with full IPv4 connectivity, receiving, processing and blocking DNS queries in your network:
Imported 596954 queries from the long-term database
-> Total DNS queries: 596954
-> Cached DNS queries: 6001
-> Forwarded DNS queries: 573711
-> Blocked DNS queries: 8848
-> Unknown DNS queries: 8394
-> Unique domains: 1361
-> Unique clients: 7
-> Known forward destinations: 4
Depending on your previous DHCP server's lease time, it may take a while for all your clients to pick up a new IP address from Pi-hole's DHCP server upon lease renewal.
You can enforce lease renewal for a client device by disconnecting and reconnecting it to your network, or by restarting or powercycling it.
One thing to note:
You are using your Pi-hole as upstream DNS server for Pi-hole:
When Pi-hole actually uses this entry as a forward destination, this will close a DNS loop, where queries circulate endlessly until the client times out.
You should remove that entry via Pi-hole's UI at Settings | DNS.