Some of my chests from my 1.12.2 world have their contents changed in order when updating to 18w08b.
This was originally reported as MC-122625. I can confirm the original fix did work, but has since regressed in one of the recent snapshots.
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duplicates 1
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MC-122625 was re-fixed in 18w19b
Sounds very much like MC-122625.
Did you open this world in any other snapshot before this one, or did you go straight from 1.12.2 to 18w08b?