after i set all devices to static IP, no firewall or anything like that, still 2 of 4 360 could not find the plex server , and xbox one could not direct connect and only securely, resulting in horrid playback quality
so this is what i did on win10 server side :
disabled secure connection , default is preferred (this seems to fix the low resolution issue on the xbox one)
added the IPs to the never require login list , separated by commas
and fixed the IP in DLNA (most important) every time your computer got a new IP assigned by your router , the original IP stays, and so confuses the xbox about the location of the plex server
it looks like this :
IP=192.168.0.100,DirectPlay=true,DirectStream=true, blablabla
i only changed the 1st IP to the static IP of my server, and boom suddenly all xbox’s started working flawlessly , there are other IPs in the command line, i did not fixed those as i was glad it finally works flawlessly
i hope this helps 
