Thanks! :)
On my screen, the painting wasn't there for the illuminati meeting. It was just a whole in the wall. There was also nobody at the table. I am in 1.12.2 if that affects anything.
Edit: Only ONE remains! The Infamous Build Team Room!
OLD -- I've grinded countless hours (about 3) and managed to discover not 50, but 32 of the 36 discovery locations.
I am asking for hints where the following 4 locations are for those who know of their location. I found them all so far...