The buffer.unpack_chunk_section loads the LightArrays and BlockArray as a tuple (due to the use of the struct.unpack function).
Due to the immutable nature of tuples, it is not possible to use the modify the data in the BlockArray, even though the setitemfunction implies that this should be possible.
I've fixed the issue locally by converting the tuple into a list before initialising the BlockArray and LightArrays.
The buffer.unpack_chunk_section loads the LightArrays and BlockArray as a tuple (due to the use of the struct.unpack function). Due to the immutable nature of tuples, it is not possible to use the modify the data in the BlockArray, even though the setitemfunction implies that this should be possible.
I've fixed the issue locally by converting the tuple into a list before initialising the BlockArray and LightArrays.