Serialization in Unity will create an instance of ConstructorAPICallBehaviour MonoBehaviour by invoking the default constructor. The default constructor calls GameObject.Find, which is not thread safe.
Method called during serialization
<Unity API method> is not allowed to be called during serialization, call it from Awake or Start instead. Called from script '<script name>' on game object '<game object name>'
Below is an example of a case which will trigger this error.