I have four swords of Twice Born and 3 pieces of Twice Born armor. I'm using the Mundus Stones Shadow and Thief. The game allows me to receive both Stones and I can see them in my character stats. When I travel to another territory either by foot or by wayshire I loose the 2nd Mundus Stone. I can travel to different wayshrines within the same territory without losing the 2nd stone for 10 mins or so but eventually the 2nd stone falls off. Swapping from bar 1 to bar 2 while wearing 3 pieces of armor doesn't remove the 2nd stone.

This doesn't seem to be the case when wearing 5 pieces of Twice Born Armor.
Logging in and out of the game removes the 2nd stone.
I've tried removing all my gear and adding it and then adding the stones again.
I've got a different stones and then added the Shadow and Thief.
I've picked up the Shadow and Thief from different territories.

Playing on Xbox One