Here's a copy of my full bug report for anyone interested or having the same issue.
Description
Random Disconnects MS Family Share via LAN (Private/Public) WIN10 Version (Latest build as of 04/19/2018 game pass expired on sub accounts this date)
I have done a full network check to make sure there was no conflicts, all devices are hardwired, and my router is in charge of UPNP with my internet modem being in full bridge mode.
Here's the Teredo info shown on each PC:
netsh interface teredo show state
Teredo Parameters
Type : natawareclient
Server Name : win1710.ipv6.microsoft.com.
Client Refresh Interval : 20 seconds
Client Port : unspecified
State : qualified
Client Type : teredo client
Network : unmanaged
NAT : cone
NAT Special Behaviour : UPNP: Yes, PortPreserving: Yes
Local Mapping : 192.168.1.x:60336
External NAT Mapping : xx.xx.xx.xx:60336
(xx are inserted to hide my external IP address)
Reproduction
* Step 1: Host PC (Main PC Account)
* Step 2: Invite family accounts (2 LAN family gamertags)
* Step 3: Join using 2 LAN Family Shared PCs
* Step 4: One of the 2 above Family Share Authorized PCs will just randomly close to desktop, they can be reinvited but then either will just repeat again after 10-15 minutes.
Note
I had initially thought this was a game or nat issue, however after seeing others using Microsoft's family game sharing functionality having the same issue in other games I think it is a flaw in the sharing authorization system leading to app closure.
Xbox One X set as home with main account credentials won't crash (when played using a different family member gamertag), PC with main credentials won't crash, only family shared PCs using their own gamertags crash.
