The config I posted here is almost complete. traefik is easier then Nginx but there are working examples around.
As I referenced already my setup is to have plain http behind the proxy (don’t want additional complexity of TLS within application container).
the only idea I had was IPv6 but as you are confident this is not an issue… I have no idea as well. I think you have to go the long way and troubleshoot one piece after another using debug logs of the applications and reverse proxy - there must be something different…
BTW I don’t remember did you test mobile browser? For me it works less good than NC mobile client - the doc opens and edit works but all the menu items are not there (Android 12, Firefox).