I was on my long time survival world I had for one closee to one year and there was chuncks I loaded befor update and now the cbuncks are now just missing gone and the Y level is messed up also but cause below Y level 17 in the neather there is just a void you can fall do w the void but there are invisible blocks that stop you at negative Y -20 and you just take damage and there was a neather fort but were my old neather portal was and not the neather fort is all gone but only a few parts of the neather fort are there but 90% of the neather fort is missing and I I had to take a guess every chunck I loaded 95% is missing or/and the Y level move up a chunck a little bit.