Certain chisel blocks (e.g. limestone, basalt, marble) are made invisible by bloodstains atop them where a player or mob has fallen to death.
This has been around for several versions, but it's difficult to say what the possible solution might be as I don't know which mod it is that adds the blood stains.
Of course, the easy in-game fix is removing the bloodstains, e.g. by mining and replacing the block!