There is this really weird glitch where if you download a world from a site (the world i used was an older version of the tutorial worlds on console). What happened was Mobs from the overworld such as Creepers, Zombies, Skeletons, and Spiders would spawn in the nether. I have proof https://www.youtube.com/watch?v=s848O6bWB6E . Also the red nether fog was overworld fog. New nether chunks would generate past that area and nether mobs would spawn in the new chunks. The world I downloaded is here in this link: https://drive.google.com/drive/folders/1_BoNyAm568ha-uz-yPKNF7tCucaj255P . It was in TU31.