If you place an ender chest in the nether, and then quit to title or go to the overworld, the ender chest will sometimes appear invisible when you return to nether. The outline of the ender chest will however still be visible if you hover over it with your mouse, just like any other block (You can see this if you watch Screenshot 1 closley). The purple particle effect will however always be visible

Placing a block next to the ender chest to cause a block update seems to make the chest visible again. If multiple ender chests are having this bug, they will all become visible again if you place a block next to only one of them(Screenshot 2).

It appears to be that only some ender chests become invicible, while others are "immune" to the bug. I do however notmanage to specifies this further.