1. The script on the prefab has a reference to a sub-object on the prefab itself. In the prefab edit mode on the Unity 2019 version, you can see that this reference exists, but directly select the prefab and look at the Insperator panel. The script reference does not exist. If there is no missing, it is none. There is no reference to the instantiated prefab.
The reason is unknown. The solution is to delete the prefab, pull it from the repository again or enter the prefab edit mode, blank the exception reference on the prefab script, and drag and assign it again.