I have been asking around in my communities and even on Twitter for an answer to this ongoing issue that I have been having for a couple of weeks now. Not sure how to explain but whenever I enter the nether portal and come back to the overworld, there appears to be something happening in just one area of my map and the only way to get rid of it is to travel south of the area and then go back north and it will correct itself. But I also had changed texture packs just to see if that was the issue but unfortunately it affected my pig's texture and it seems to be missing completely. This is a recent problem that I've been dealing with for awhile ever since the last update I believe.