Jellyfin stuttering over VPN despite fast download speed

[StaticUnit97]

Hey everyone. I've been working with my brother to set him up with Jellyfin on my local server, but we have been running into some pretty severe stuttering on his end. Videos are playing smoothly for a few seconds and then pausing to load/buffer for a few seconds, and repeat. We've seen this behavior across a number of titles.

Some relevant info:

• Server is running Ubuntu server 24.04, has an i5-9500T, 8 GB RAM, and Jellyfin (v10.10.0) is running via docker on a 256 GB SSD
  
• Using the Speedtest CLI tool, the server is getting 820 mbps up and down consistently
  
• He is connecting to my network via a Wireguard VPN (wg-easy via docker specifically) on a Windows laptop and an Android phone. On his local network, he is getting ~120 mbps down over the VPN connection. He lives about ~100 miles from me.
  
• He is using the Jellyfin Media Player on Windows, and the integrated player on the Android app.
  

Some things we've tried:

• We've tried a number of titles, and all of them are direct playing. Highest bitrate title we've tried is ~68 mbps, so well within the download speeds he's getting.
  
• If he forces the player to 20 mbps, all videos play fine. This seems strange, since he's getting ~120 down on the VPN, so you would think all titles would play fine.
  
• We've played with various Wireguard MTU values. Some make it much worse, others are at best the same as the default.
  
• I've been able to run all titles fine on my Android phone over the VPN on a cell connection.
  

Does anyone have suggestions on what to try next? Is this a problem with the Jellyfin server, client, or Wireguard? I'm having trouble identifying what the bottleneck could be. Based on the fact that forcing the bitrate to 20 mbps works makes me think it's a networking issue, but this is not reflected in any of the speedtests we've tried. Any other ideas?