When opening a 1.7 world in any snapshot clears storage blocks (E.g: Chests, Furnaces, Dispensers...) and removes paintings from walls.
Related issues
duplicates
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Did you load this world in a snapshot then try to run an older version?
migrated
No, I just loaded it in a snapshot. It messed up my youtube series and my massive puzzle map.
Sounds like another duplicate of MC-45009