"Unable to instantiate prefab. Prefab may be broken"

I just had the same problem actually, and I don't know what to do. Whenever I try to drag the prefab to the hierarchy on 2018.1 I get that message.

I am having the same issue... I upgraded to unity 2018 , as want to use unity inbuilt Text$$anonymous$$esh Pro. and updated all UI, however now my prefab is not working as it suppose to, having same error as mention. Prefeb is too complex as its a player and enemy with animation, AI and UI... will be pain to recreate same :( is ther any solution to fix it... please help...

Same page... Any thought? I've already tried to export from U2018 but no luck.

Same problem here

I get this problem often its so annoying. I downloaded an asset other day and tried it. Everything went fine and i didnt touch that asset folder in my project since then was working on something else. Then i come back couple days or week later and try to place a prefab on the scene bam broken. Nothing changed at all. Unity often randomly give bug like this using 2018.1.1f1. It happened with many other asset. When its not its a script in my scene that get unlinked for some reason. I think i lost a whole week since 2 month trying to figure out bugs that was related to broken prefabs or missing script that randomly appear. Is there a known unity version working at best? Im gonna give it a try.