I was playing in my Minecraft world about 2000 blocks away from my base (X 2200, Z -2600) and I used a nether portal to go back to my base. I return to find many chunks unloaded, even after 10 minutes of waiting. Some mobs wandering on those chunks and were glitching out, their entire bodies shaking as it slid around. Walking on these chunks I realized there was still collision, but blocks were not making the sounds they once were (grass making stone sounds, some blocks not making any sounds). One particular spot made the game think I was in a cave and darkened my screen. I know there already are posts about disappearing terrain, but this seemed to only be failed chunk loading, instead of actual map corruption.