When entering prefab mode for modification, Pre-fab-mode A red line is created as a screenshot and the structure is destroyed. I upgraded the Unity version and used the new Prefab mode, I get this error. How should I fix it ?? Scene View and Game View are fine but only in prefab mode It is destroyed like that. I am currently using version 2018.3.7, but I am more familiar with the prefab function of previous versions ..... I need advice.
Try to upgrade to 2018.3.12 or later. Some issues related to Canvases in Prefab Mode were addressed there. I don't have enough info from your post to be sure if it will help or not, but it's worth a shot perhaps.