@Kris I installed latest Ubuntu 18.04.4 Desktop in VirtualBox v.6.0.16 (on MacOS 10.15.3) with only NAT network interface connected, applied all available updates, run the script mentioned above and it works.
The weirdness in api-gateway logs is that the following message is repetitive.
setting up automatic reload on host IP address changes for DNS names: mender-useradm mender-inventory mender-deployments mender-device-auth mender-device-adm mender-gui
Here in api-gateway entrypoint script this echo which prints the message and there are no any loops, so, it should not repeat.
Can you try stop everything by ./demo down and then in one terminal tab run the following:
docker run -it -p 8888:80 openresty/openresty:1.13.6.2-0-alpine
and in another terminal tab execute:
curl -X GET http://localhost:8888
And post the output from both terminals in addition to dmesg output.