Just setup unraid and this docker and I am experiencing similar issues.
On LAN, I have no issues streaming/transcoding anything but when I'm connecting remotely, I cannot play any files.
The files will play for a few seconds then buffer. Switching the quality of transcode does not help.
Before I switched over to unraid, I was using an Nvidia Shield TV and was able to watch remotely without this issue, so I do not think this is a network issue.
Any help would be greatly appreciated. Thanks!