There seems to be a rendering issue when looking through/behind the new text display entities. Sometimes mobs are not rendered properly when looking at the entities through the text's background. As mentioned this only happens sometimes but I have been able to reproduce fairly consistently with spawn eggs.

Upon further testing, it seems to affect tile entities too such as chests.

The command used to summon the text shown in my screenshots is:

/summon text_display ~ ~ ~ {billboard:"center",text:'{"text":"This text is blocking some entities but not others for some reason?"}'} 

This seems like it could be related to MC-197328 which was Fixed a couple years ago