[Xbox] Unable to invite to guild

I have been trying to invite a player to my guild for a few days now, but he never receives the invite.

I've tried the RS-dpad method using user name and the direct communication 'invite to guild' method with him both in and out of the party and none of these methods showed an invite on his screen.

This Xbox is on the same network as my Xbox.

My other friend (also on the same network / but a different Xbox) was able to join the guild without issue a few weeks ago before the '3.18e' update.

All Xboxes are hooked via ethernet cables.

Please advise.

Thank you.