First of all, this occurs in Minecraft Java 1.16.3 but the affected versions will not let me enter 1.16.3. It says Version with id '1.16.3' does not exist.

The issue:

I found an issue that while in spectator mode entity properties disappear. 

In the first photo, I am not in a block but behind orange glass in the nether. The writing on the left sign disappears. This had nothing to do with chunks or render. The text in the sign to the right is fine.

In the last photo, I show that if I move forward out of an enclosed structure the text appears.