So this is my first reply but I figured out a solution to this issue. What appears to happen is when you log into unraid, it uses a URL rewrite to the host name. Why it happens when I have authentik setup, I really dont know... I dont have all the answers, I just have a workaround that I love.
I went into unraid, management settings, then changed the Local TLD: to my domain name. ie domain.com
My servers name is Unraid, so the Local access URLs: is now Unraid.Domain.com
I am using ubiquity so there is no DNS... so had to fix problem 2. I installed a pihole but you could use the bind docker to setup a basic DNS server. Pihole worked very smoothly for this and I wanted to build one either way. I then went to the DNS option, and hostname is Unraid.domain.com and then obviously the local ip of my unraid server.
I then shut down my docker and vm services, went into the networking, changed my first DNS to the pihole, then second dns to an upstream dns server.
Turned on the docker services, powered on the pihole first, then powered on the rest of my Dockers to ensure they used the pihole as the primary DNS.
Then in NPM, I changed the forward hostname as Unraid.Domain.com.
I think the main issue we are having has something to do with dockers being able to reach the hostname of the unraid server. Its not on the docker network exactly. Either way, this method worked very smoothly for me. I really hope this helps.