Just to clarify, [SerializeField] did something; it was serializing the blackboard, but through FullSerializer (which is the custom serializer used in NodeCanvas). The change to [fsSerializeAs] has practically no difference at all, because both [SerializeField] and [fsSerializeAs] do exactly the same thing as far as FullSerialize handles them.
Do no remove the attribute. It is required to serialize the blackboard.
I have tried opening old projects and everything works as expected (there is honestly no reason not to since both attributes do the exact same thing Full Serializer wise). Could it be that your get the errors because you removed the attribute first and then re-added?
Gavalakis
