This was my post, and what I marked as my own solution does not work anymore. I had to start from scratch with my setup and I'm encountering the same issue. I can't unmark the previous solution, but it definitely doesn't work as I said it did.
Continuing the discussion from External Custom Domain inside LAN:
Please follow the below template, it will help us to help you!
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:
[Replace this text with what you think should be happening. Please include as much detail as possible including, but not limited to:
-operating system
-hardware]
Actual Behaviour:
[replace this text with what is actually happening]
Debug Token:
[Replace this text with the debug token provided from running pihole -d (or running the debug script through the web interface]