Going from the Nether to the Overworld is very slow

I have a survival world with many bases spread across vast distances. To reduce my pain, I made a Nether fast-travel system, using portals all over the place. Sometimes, a chunk in the Overworld never loads, and will never load no matter what I do. When I try to enter the base from the Nether with the fast-travel, I am stuck with the Generating World, Building Terrain screen, and I am stuck like that for a long time. Please fix it because I want to see my base again.