I found when trying to craft a shield that the shield wasn't appearing. I thought the crafting recipe was changed or something, but with investigating in creative mode, I found the item was there and the recipe wasn't changed or bugged, but that the shield themselves are invisible.

I then tried holding one in my hotbar and trying to block a Skeleton (which I spawned) and it's arrows. The shield still functions just fine. However, it's disconcerting that it was invisible as I was unable to tell if the shield was actually up when I held the shield. mojang pls fix

However, I'm not sure if it's related, but for some reason double chests and equipped helmet and chestplates also suddenly became invisible. Quitting the world and then logging back into your world doesn't seem to fix it, either, as it also persists between all worlds.

Apparently restarting Minecraft fixed the issue, but I am unsure how to recreate the rendering bug.