I think this is an Emby issue related to .net core, from Emby forums:
The problem is most likely due to another DLNA service running on your NAS device.
** Normally co-existence wouldn’t be a problem, a you’ve seen with Emby 3.3.**
**But there’s been a regression in the .net core framework since .net core version 2.1 and it persists in version 2.2. **
Emby 3.3 used .net core 2.0 (or maybe MONO) where this problem didn’t exist.
Unfortunately there’s nothing we can do about it. MS has already fixed this for .net core 3.0, but it’s not yet released.
Your only option at this time is to disable the other DLNA service on your device.
https://emby.media/community/index.php?/topic/28502-emby-not-workin-on-dlna-device/?p=667878
Yes, Plex works fine, I have moved on from Plex to Emby.