When placing or updating redstone under a double chest, the chest will separate (this includes the blocks on bottom diagonal of the chest).

Upon removing redstone on the bottom left diagonal of the chest, the chest will separate with the left side maintaining its double chest texture, and the right side shrinking back into a single chest.

Upon removing redstone on the bottom right diagonal of the chest, the chest will separate with the left side being a single chest, and the right side becoming invisible.

Tests done in macOS, Minecraft 1.13 - Pre 7

2018-07-12 06-21-04.mp4