Issues accessing Jellyfin over HTTPS from LAN with iOS/Google TV apps

[PlugOut]

Hi everyone,
I’m trying to set up Jellyfin with HTTPS in a clean way, but I’m running into some problems when accessing it from my internal network using the official apps.
Current setup

• OS: Windows Server 2019
  
• Domain: I have my own domain configured
  
• External access: works via
  mydomain:port
  (UPnP rule automatically created by the router), but only over HTTP
  
• Certificate: I already have a valid SSL certificate for my domain (issued with win-acme)
  

The problem

• When I configure Jellyfin to use HTTPS with my domain certificate, I can connect from outside my network, but from inside the LAN the official apps (iOS and Google TV) fail to connect.
  
• Access via browser works fine both internally and externally.
  
• I also tried putting Jellyfin behind Nginx with a subpath
  /jellyfin
  :
  

• Works fine in the browser
  
• Same issue with the apps: they refuse to connect
  

Question
What’s the correct way to configure Jellyfin with HTTPS on Windows Server 2019 so that:

• The official apps (iOS, Google TV, Windows) can connect both internally and externally
  
• I can use my domain with a valid certificate, without relying on subpaths or non-standard ports
  

Thanks in advance for any help

[schnappi]

1) Does your network have the same domain name as the domain name of your Jellyfin server? For example, most network have a domain, such a .lan, .local, ect.

2) Are you using a custom DNS server?

3) Add a single custom DNS server (just use 9.9.9.9) on one of your iOS devices that is not working, does this solve the problem?

4) Run a trace route from the iOS device that does not work. May need to download an app, but it can be done.