Are you certain that the asset in question, is not referenced anywhere in the graph? If it is not, then when the graph serialize it should clear all references that are not really referenced anymore.
Could it be that you are using the local graph blackboard instead of the GraphOwner blackboard component for referencing the asset in question? If so, the local graph blackboard is serialized together with the graph (same json). It seems like this could be the case here, but let please me know.
Gavalakis
