I have a clean installation of CentOS 8 server, and have only installed snapd and then MAAS. I am using the maas-test-db snap as database. Didn’t get any errors or warnings during the installation and followed https://maas.io/install, but couldn’t do step 5 due to the web interface not responding.
I had forgotten CentOS 8 uses nftables instead of iptables, and since iptables showed as accepting everything, I had ruled out such potential problems.