We’ve been doing some more tests, and we had the same issue with any HTTP server running from that Windows Server 2019 and other HTTP clients running on an Apple platform, even if they’re not related to video. For example it also happens with VLC on macOS playing a video from a simple HTTP server running from Windows Server 2019.
More specifically we tested serving a movie file with an nginx server, and download it from macOS using just curl, since that removes all the “video playback” stuff and simplifies our investigation, and we had this very same problem. So it doesn’t seem to be a bug in any of the Plex code, but either on the Windows network stack or Apple’s network/HTTP implementation.
Our expert @Ridley digged into the exact packet exchange between client and server and noticed Apple code was doing something unusual but allowed: “the client -macOS- appears to be deliberately delaying ACKs for full-sized segments beyond the 2 specified in RFC 1122, but that’s marked as a SHOULD, not a MUST, so it’s not out of spec”.
So for now we think this is a bug in Windows Server 2019, we haven’t found any workarounds for it yet, so right now we can only suggest to avoid using Windows Server 2019 if you have any Apple-based client.
