MCD / MCD-3570

I keep getting join session failure errors when attempting to join friends in games. When a friend attempts to join my game, they receive "connection timeout the connection to the host timed out."
We were able to play a week ago with no issues. All on the same network, win10 version (launcher), but since the reconnect button was added (I don't recall it being there previously), it seems this has been a problem but doesn't effect everyone.

This is not due to Microsoft/XBox account settings, there are no restrictions at all.

I uninstalled, restarted, reinstalled. No change

Logged in on a different machine, was able to join game.

Friend logged into their account, ran through tutorial on my computer, was not able to join games/I was not able to join their game.

Created firewall exceptions, no change.

Disabled firewall/AV/EPUP applications, no change.

Disabled any/all UAC on local machine, no change.

Checked for corrupted user profile, removed and created new profile, no change.

Ran chkdsk, no issues.

Ran sfc, no issues.

We are all on the same local network. No network related issues with this machine, all other games and services connect normally/correctly.

I can play it solo.

Are there logs created by MCD that I can check? I haven't found any immediately.