When you do setblock a chest next to a double chest, it will make it invisible and break the GUI of its chest, and the others.
MC-73807
Setblock with Chests bug
Resolved
Invalid
0
Placing more than 2 chests of the same kind next to eachother is not possible in vanilla mechanics, you are forcing that behaviour. The game tries to combine them but doesn't know how to properly show it.