Okay, so I had all the Dragon Priest masks including the ones from the Dragonborn DLC stored away in a safe in the cellar of Lakeview Manor. The new update came out so I decided to download it. When I went to grab one of the masks from the safe, it was completely empty. None of my other chests, safes etc were affected by this which is why I'm finding it so strange..

Anyone else experiencing something similar or have any answers as to where they could've gone?

Not to be snarky but they probably went to the same place that they went for me. Which is another container in another house as I started to move in but did not complete the move. And forgot what I had moved and not moved.

Also, cells will sometimes just not render correctly, it's why an entire city can disappear sometimes. Leave the cell, save, exit the game, reboot the system, launch the game and load up the save. If you go back, there is a good chance that they will be there again.

Barring that, remove the update, if possible, then load up the save, then move the masks somewhere else, put the update back on. I don't think a patch would have done this, and Dragonborne should not affect those cells.