Do you have a plex pass and do you think about using the Plex Home feature?
Remember, after setting a pin on your account or adding a managed user, you cannot use DLNA anymore!
Read up about this here:
On top of that:
There is probably an issue which I am trying to verify. If you are willing to do a little experimentation and help to identify this issue so it can be re-created and ultimately fixed by the developers, read on:
Although you can re-activate DLNA, after it was automatically switched off (by activating Plex Home) there is maybe a snag:
If you experience suddenly that PMS is now transcoding to 720p when it before direct-played, (which, on a low powered NAS device can mean the video is not playing at all!)
Deactivate Plex Home by removing all managed users and remove the PIN you may have set on your master plex account (the one with the little 'crown' icon).
Then restart plex server.
If it now plays as before (without transcoding), I'd love to hear about it.
Please gather log files from a playback attempt
before and after you activated/deactivated plex home!
(So the logs can be compared)
So it seems, that upon activating plex home, the DLNA remote preferences apply.
On the DLNA client, navigate to the folder named Settings (or Preferences, I don't remember exactly). There is a resolution preference for 'remote' which defaults to 720p. Set it to 1080p. Also crank up the 'quality' preference for 'remote'. It should re-enable you to direct stream many material which suddenly ceased to stream upon activation of Plex Home.