I have a world that I have been playing on recently through a couple snapshots. It is now on the 1.17 release and whenever I go into the nether only a few chunks load in the nether. If I try to go back to the overworld only a few chunks load too. I have not entered the nether on the world before the full update came out. The nether is completely useless as in this state. I am also using optifine.