Stream from outside the network breaks off - Issue solved?

[Burkhazad]

Good evening, everyone,

I upgraded my hardware and updated to v10.8.13 at the same time.

Since then I've had the problem that the stream stops after a while when it runs via the dynamic DNS. When exactly is different.
It didn't matter whether it was "Direct Play" or transcoding (audio only or complete)

Hardware:
MSI B550A-Pro
AMD Ryzen 7 5700G
32 GB RAM
BrosTrend 2.5GBase-T PCIe network card (due to driver problems)

Internet:
250Mbit downstream, 40-45Mbit upstream

System:
Ubuntu Server 22.04 LTS
Linux 5.15.0-91-generic on x86_64
Webmin 2.105
Jellyfin 10.08.13 (installation via repository - automatic)
Caddy as reverse proxy via Caddyfile - works

Clients:
AndroidTV 0.16.1
Jellyfin Web 10.8.13 via Chrome on PanasonicTV

Unfortunately I don't know what is meant by logs on debug level (English not my native language)

SystemLog entries:
Slow HTTP Response from "https://***/Sessions/Playing/Progress" to "109.42.***.***" in 0:00:00.8038239 with Status Code 204
AuthenticationScheme: "CustomAuthentication" was forbidden (flooding)

Transcoding runs through and is finished before the client suddenly stops. Hardware acceleration does not matter, happens both with and without it.

Is it me, a setting, the Jellyfin version? Before the upgrade (hardware) and the update (JellyFin) everything ran without any problems.

I'm wondering if I should switch to Windows to maybe fix the problem.