Is there any specific mtu or mss config for jellyfin?

[TheDreadPirate]

Can you share your fully jellyfin logs with us? Giving us an approximate timestamp will help us search the log. Sanitize any WAN IPs and user names. Upload the log to pastebin and link it back here.

The operating system handles all the transport specifics. Jellyfin shouldn't care about any network configs as long as it is consistent.

Some things to look at:

1) Are VPN devices on a separate subnet? Is that subnet in the list of internal addresses?
2) If you don't want VPN devices to be considered "internal", do you have bit rate limit for external connections?
3) Do you have hardware accelerated transcoding setup? Related to #2, if you have a bit rate limit for external connections it may be transcoding very slowly.