Using the very latest version of Plex Server and player on the Panasonic JZ1500, there is a problem that this TV (which is completely identical to the JZ2004, apart from additional built in speakers) is not included in the supported list by Panasonic / Plex.
Thus the JZ1500 is just detected as „generic“ and there is a transcoding going on when using the native Panasonic Plex app instead of providing a Direct Play.
This has been confirmed also by many other users too.
Did you find a solution for this ? My father in law just got a Jz1500 and I installed Plex on it, connected to my remote server, even though the TV is connected in Wifi 5ghz to fiber router (1 gbps down), and playback settings are set to “original”, all movies are trasncoded and seems to be limited to a 8 mbps stream. I tried UHD movies or Full HD remuxes, same thing, and weird also because during playback if I go to setting to change quality it says it’s currently playing original quality but from Tautulli I see that the stream in trancoded and limited to 8 mbps.
tl;dr the plex app has strange unnecessary hard limits (4Mbps, 2 channels, 1920x1080, …) and anything outside of that it forces a transcoding.
The media plays fine directly via DLNA.
There are some workarounds.
Would be nice if Plex added a button to the server so we could have it lie to their own app, but I am getting to the point of just dropping Plex and sticking with DLNA which works and is predictable.