Jellyfin SyncPlay doesn't work on Synology NAS server

[Blasterfight]

Hello,

* Jellyfin Server 10.8.13-13 (Synology)
* Server installed on a Synology NAS
* Using Synology's internal reverse proxy to host Jellyfin on HTTPS, the service is visible at https://<mydomain>:8090/ from my devices
* I access Jellyfin on device A and create a new SyncPlay group. Then start my Jellyfin client on my device B and join the aforemantioned SyncPlay group
* What I expect to happen: When I play a movie on device A, the stream should start on device B too
* What happens: The movie plays only on device A

Reverse proxy config:


Jellyfin config


Logs:

  Log2.txt.zip (Size: 20.8 KB / Downloads: 17)
  Log.txt (Size: 17.54 KB / Downloads: 16)