When any ring is placed in the worldspace, their textures will not load properly and instead render the item as completely black instead. This is due to the model data of rings incorrectly calling upon the wrong file extension, .tga, instead of the correct .dds filetype which is used by the textures themselves.
This quote is from the UESP website but similiar information can be found on nexusmods.com and other forums.
https://en.uesp.net/wiki/File:MW-item-Ring_of_Azura.jpg
The bug seems to be true for every ring (though I did not test every ring in the game). Some examples are the Ring of the Hortator, but even DLC rings like BlueDev's Ring of Viewing. Of course the generic enchanted rings also show this bug. The bug happens for both rings placed by the player and rings already placed in the world by the game.