In 1.12, Spigot improved their blockstate implementation to take a full
copy of the TE, this allows for a much better snapshot in that it will
actually retain all of the TE's state, it is a much more expensive
implementation. This is also implicated with their backwards compat
for inventories meaning that accessing of a snapshots inventory of a
placed block will actually access the inventory of the live TE, making
creation of a snapshot redundant if the only intent is to interact with
the TEs inventory.
Hoppers are a horrible hit, every attempt to transfer an ItemStack will
result in two TileEntity snapshots, with two hoppers and a double chest
ontop, I managed to log 380 cases per second where a snapshot would have been
taken in cases where the snapshot is redundant.
Shane Freeder