So after I played on Jigarbov's Redstone Tutorial, every world got their items deleted, armor, and got set back to spawn.
Thankfully I just had to quit the game and come back, but this is one of the scariest bugs ever.
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Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-29863.
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==== MORE INFO on the bug ====
It only triggers when you join a multiplayer / realm game and return to your world. May also be the case with marketplace maps.