Ever check your canvas color mode? Mine was set to CMYK from some old print file, and every screen export came out dull and muddy until I switched it back to RGB. Settings you never touched are always the sneaky ones.

I read once that masons used to leave all kinds of stuff in cornerstones, like coins and old newspapers and even bottles of whiskey sometimes. There was a story from somewhere in Pennsylvania about a guy who found a whole time capsule from the 1890s with a newspaper still readable inside. Putting the note back was a good move if you ask me, it felt like it belonged there. Some folks might say leave it be and others might want to keep it, so your call really. I've never found anything in a wall myself but now I want to go poke around my uncle's old garage.