(Case 1081636) Prefabs: Failed to save changes and log errors

Prefab cannot be saved anymore if there is any script reference breaks and when u select a child object, it will keep logging errors. I think prefab should still can be saved just like previous Unity as sometimes ppl have to rush to change something and no time to fix the missing reference error then inform user about the missing reference.

 

2018.2 also did not allow to save prafabs with missing scripts.
You probalby lost prefab script reference due to unity bug related to prefabs that is already reported.