This is essentially that occasionally block entities (shulker boxes, chests, player heads, etc) will fail to render in the world. The only indication that they exist is their collision, shadows around them, and the box drawn when they are hovered over. In my experience this has only happened consistently in 2 locations.

1. A tower in a personal server had 3 shulker boxes that would not ever even if replaced.
2. On hammerSMP nether roof there is a set of shulker boxes that don't render. This is also not specific to my instance as a fellow Hammer member PapiChase#0837 had it happen to him as well.

Poke#8236 helpfully pointed out this is specifically when a subchunk with no blocks other than block entities is rendered.

For both me and papichase, sodium was compiled against latest commit. My build was compiled and used in java 14. Papichase's build was compiled and run in java 8.

I will include more screenshots and info soon.

Works properly in latest commit

yeah also had the same issue, but from my observation:
1 it affects certain chunks (tile-entities continue rendering over the chunk border)
2 issue sometimes disappears and then reappears in the same chunk