So, uh, yeah, I went to update one of my in-game maps, and when I did, I saw a lot of grey blotches all over the freshly pick-blocked map.  They were all the same shape, size, and distance from each other, creating an almost static appearance out of my perfectly good map!  I need that map for my base, and now I don't want to pick block or even create another map for fear that this will happen again.  Java is running perfectly, I checked, not sure if it's the latest version or not though, and the OS is Windows 10 running Minecraft Java Edition.  Oh, and my GPU is a Nvidia 1050ti.  Hope this helps, and I won't be attempting to upload images as I don't want this same thing to happen again to any of my other in-game maps.  Rockatoa, Brickticks out!