Hello there, I was building a snow city town on old world and suddenly I was unexpectedly seeing that there was random blocks on the polished andesite. (Mostly it happens in the snow biome)
When I remove and replace polished andesite to the area, it came back several minutes later and it still won't go away. (Same applies to other areas where they still occur.)
I remembered years ago it never happened but I realized this was truely a bug to me.