Hello, we import all our project from 2017.4 to 2018.3 to test/use the new nested prefab system. And it seems to work well in 9/10 cases (hopefully). But we encountered a main issue with one of our prefab whereas this one seems to be equivalent to all others prefab we have. At the end of import process, we get thoses errors/warnings in the console : - CheckConsistency: GameObject does not reference component Canvas. Fixing. - Prefab “MenuIntelligentThing” has multiple roots. We’ve upgraded your prefab to work with the new nested prefab structure, but please verify that this is the behavior you intended to have. So I supposed the first error which quite incomplete (is triggered by the warning) cause we don't know which GameObject triggers this. We will have an improvement on this in a later beta ? But when I check the prefab before import process, there is no multiple roots so I don't know why the importing process in your 2018.3 triggered this, any idea ? And in our project hierarchy the prefab looks like this since unity 2018.3b4 : Thanks for any answer we could obtain on this. Aurélien.