HTTP 204 after upgrading from 18.02 to 20.0.3

changing nothing except the version, the configuration that works for me in 18.02 does not work in 20.03 (nor any other version I’ve tried after 18.02). When I select the admin console link, I get the spinning “Loading the admin console message”. Looking at dev tools, it dies with a 204 on the following:

https://qmi-keycloak20-7efe9f.qmi.my-poc.com:4993/realms/master/protocol/openid-connect/login-status-iframe.html/init?client_id=security-admin-console&origin=https%3A%2F%2Fqmi-keycloak20-7efe9f.qmi.my-poc.com%3A4993

Here is my config:

hostname-strict=false
hostname-strict-backchannel=false
hostname-strict-https=false
http-port=8080
https-port=4993
hostname-url=https://qmi-keycloak20-7efe9f.qmi.my-poc.com:4993/

Any ideas? It seems many people have issues with recent versions and most seem to give up and go back to an older one. I am using a commercial certificate and there is currently no reverse proxies or WAFs in the way (I will need to add a WAF later, but want to get this working without first).

NB: " ./kcadm.sh config credentials" works for both http and https.

Thanks.