My wife and I play together on a single Xbox One console (split screen), non-xbox gold / live accounts. We will play upwards of 8-12 hours at a time and always doing random things in different parts of the world. Since upgrading to the BTU we've noticed serveral things happening.

1) Upon savings and exiting (both characters, 2nd player first). We can login and 90% of the time the 1st player is exactly where they last logged off. The 2nd player has a 30% or less of a chance of this happening. In fact, the 2nd player is typically several hours / days behind. For example, 2nd player has 30 points + lots of items and saved in the house we created. Logout/in and now you have been reduced to 0 or 7 or 9 points and you are in some random mine you once were in.

2) Using the above example, we've started having 2nd player give all items to 1st player before logging out and saving. This is where the 90% from above comes in, after doing so 1st player will still have all the items after relogging into the game and be exactly where you left off. However, sometimes you are put back at the world save and have 0 points.

3) Both 1st and 2nd players can be running around the world investigating. Then all of a sudden you can see the stars under the world (does not matter what time of day/night). If you wait a moment, the stars go away and now you can see under the world, IE: mines, lava, etc... At this exact moment both players will for certain loose all they have done for X long ago. If both players save and logout/in then both players are typically set back to an auto-save point several hours prior and you're also placed into a random location on the map.

We only play together, never online, no realms.. just plain old minecraft in survival mode.

We can replicate this on a daily basis too.

Hard-resetting the xbox by holding the power for 10+ seconds has no effect on how the game play works.

On a side note, #3 typically happens to the 2nd player first in most cases. We've noticed this typically only happens with the 1st player if you are in a boat and over large bodies of water while looking down at an angle to see under the water OR if 1st player zones into the nether.