I am playing minecraft currently on the snapshots, and i looted a desert temple. When i came back later for some looot I hadn't picked up yet, the whole temple had reset. All the blocks were back where they started and all the chests were full again. It was the same temple, as I looted the village next to it. This all wasn't reset.
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I had something odd happen to me, too. I built a 1x1 tower in a field, and kept tping back to the top of it.
After around the 10th teleport, the tower was gone. In fact, everything I had built nearby was gone. Same field, same exact co-ordinates. It seems the chunks just regenerated fresh.
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We're tracking this issue in MC-216148, so this ticket is being resolved and linked as a duplicate.
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Could you share your launcher log?