I experienced similar issues with MiaB behind pfSense, and received no help on this forum. The project is currently very narrowly focused (in my opinion, too narrowly focused).
My purpose was mostly just to test MiaB as a project and the project performed flawlessly except for this one issue.
I did not modify any network settings on the server, but did configure pfSense to open ports (except 53) to MiaB, plus I used an external DNS server.