Connection Issues in FireTV and Andoid Apps over the Internet

[gerrlaf]

Hello everyone, 

I have been researching for a while now, but I can't seem to find a solution to my problem. 

I am experiencing connection issues with my Jellyfin server when using Android devices and Fire TV from the internet. 
Initially, with the setup I’m about to describe, everything worked fine for a while. I’m not exactly sure when it stopped working. Since then, several Jellyfin server updates and firewall updates have been made. 

I host a Jellyfin server in a DMZ, which I use internally (LAN) as well as via the internet on HTTPS port 8920. I have a valid certificate from Let’s Encrypt. 
Before the Jellyfin server, I use the Sophos XG Firewall as a web application firewall. It supports TLS 1.2 and 1.3. In front of that, there is a standard router with the necessary port forwarding. 
The firewall accepts requests from the internet on port 8920 and forwards them to the server on port 8096. I wanted to avoid managing certificates on the server since the firewall handles them automatically. The encryption thus terminates at the firewall. 

### What has stopped working for some time:
- The Jellyfin apps on Fire TV and Android when accessed from the internet via port 8920. Kodi add-ons do not work either. However, the connection works via a browser on these devices. The app reports that no connection is possible. As soon as I also allow port 8096, it works—though unencrypted, which I do not want. 

### What is still working:
- The apps work on iOS devices. 
- Everything works via a browser, whether on Windows, Linux, iOS, Android, or Fire TV. 
- The Jellyfin apps on Fire TV and Android work when accessed from the LAN using the internally reachable IP. 
- Firewall logs show no blocked connections. 

Any ideas?

[bitmap]

How are you accessing outside? Via FQDN or public IP?

[gerrlaf]

I'm accessing via FQDN.