After leaving the nether on a multiplayer server granite blocks visualized in the world but they aren't actually there, I have been in and out of the nether several times and this hasn't happened before, I had recently been killing wither skeletons blazes and magma cubes before coming into the overworld again if that helps. They visually appear every 16 blocks on the z and x cords, I included screenshots of the f3 menu while under two different sets of blocks that are next to each other, also they disappear slightly when you hit f3 and a. I included a screenshot of this as well.