We have been experiencing this issue as well.
Similar set up, MCPE Windows 10 1.2 hosting the game with two Xbox One (splitscreen) players. Unfortunately for the XB1 users their inventory (as previously described above) is hit or miss.
Both devices are on the Better Together Update
Robert A Petit
We have been experiencing this issue as well.
Similar set up, MCPE Windows 10 1.2 hosting the game with two Xbox One (splitscreen) players. Unfortunately for the XB1 users their inventory (as previously described above) is hit or miss.
Both devices are on the Better Together Update