When I attempted to bring the Texas Hold'em prefab into my world I noticed that the buttons did not have text on them, I moved some stuff around and noticed that the text was still working but was getting overlayed by the background underneath it. After creating a new prefab and double checking the import I still had the issue of the background texture of the buttons overlaying the text.

 For some reason whenever the world is built it will set its material to be 4000 render queue when it needs to be 3000 for it to show the text above it. Anytime I manually change the render queue back to 3000 it would reset back to 4000 upon building the world to test. Another thing that was odd is that the back button in the local settings area had their icons however the join button and the number pad as well as the local settings panel did not have their text or icons, basically everything that had text to it would be hidden under the background overlay but anything with an image like the back button did not get overlayed.

Fixed! Changing text material to Supersampled UI Overlay

Update, I did manage to figure out a fix for this, as it seems something within my world is automatically setting the render queue for the Supersampled UI, that the background of the buttons uses, to 4000 even after I changed it. I found a fix by just changing the material of the text itself to Supersampled UI Overlay instead and that seems to have fixed things.