When attempting to place a double chest on top of another double chest if the user clicks on the top of the bottom chest rather than the side of the top one the chests do not connect.
When attempting to place a double chest on top of another double chest if the user clicks on the top of the bottom chest rather than the side of the top one the chests do not connect.
This is how it's is in 1.13 if you hold down Shift then the chest will not connect, place a block behind or next to where you want to place it then click on the block instead of the chest on the bottom.