I've seen this issue reported back in version 1.14, and was said to be resolved. Haven't seen this issue reported for 1.16 yet. I have pulled a ghast through a portal several times, and it has not travelled to the overworld once. This makes obtaining the Uneasy Alliance advancement impossible. note ; Playing in 1.16.5 optifine, Hardcore world, using enchanted fishing rods to pull the ghast through.