With your VLANs, Plex considers the connection from the client to the server to be remote… hence applying remote streaming restrictions (e.g. applying “remote quality” instead of “local quality”). If your remote access setup is messed up / not working, the stream might get redirected through a Plex relay server (“the internet”).
If you depend on having server and clients distributed across different subnets/VLANs… at least tell Plex that those other VLANs are supposed to be considered as local networks.
Settings > [Server Name] > Network > LAN Networks
If that’s what you mean by “I have going into Plex’ setting include my VLANs in the Network list” – please double-check the notation is correct (no unnecessary spaces, letters/digits…). Also verify the clients are allowed to access your server through the different VLANs.
https://support.plex.tv/articles/200430283-network/
