There is a wee bit of a problem with the way Composite Chests render, or at least composite double chests.

Now you see it:

However, turn ever so slightly to the right and...

Now you don't.

A little more experimentation shows it is only on double chests and only on the right side of those double chests. Left side renders as expected.

Already fixed in a side branch, this will hopefully soon get merged into the main one :)