I believe creative mode is still in the experimentation stage, so it's bound to have a fair share of problems. Try starting a new save or reinstalling the game, other than that, I guess wait to see if the dev's get around to fixing it if you can't get it to work.
(The dev's are probably getting a lot of notifications about problems left and right, just be patient, I'm sure they'll get around to helping out you and anyone else having this problem )
We should have the new version next week but in the meantime this is a bug and the solution offered in many many places. Delete your game, reinstall, resolved. You will not loose your save and if you do not use the game menu to exit it should not happen again. To leave the game without making an issue use the xbox button, menu, quit from there. It is something to do with the in game logout menu broken
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(The dev's are probably getting a lot of notifications about problems left and right, just be patient, I'm sure they'll get around to helping out you and anyone else having this problem