Continuing the discussion from Error on preview only behind proxy/load balancer and also Kobo form could not open, I am witnessing degredations of Enketo Express when using it on a local installation.
I can reproduce both errors that are described in the original postings.
kf.kobo.local tries to access Enketo via its IP, and not via the hostname. Therefore
nginx cannot associate the request to the desired service and fails to
proxy_pass to the correct upstream.
kobo-deployments would be the place to configure the value
10.10.10.240 in my example above to point at