Hmm. Do you maybe have any other asset (or your own code) that is using a namespace named “Hierarchy” and thus creates a conflict?
Can you please try in a new project and let me know if the problem persists?
I have just send a new version to the asset store a few hours ago. To resolve this issue, I have also renamed the class “Hierarchy” to something different, so that this conflict is resolved. Please update to the new FlowCanvas version as soon as it goes live.
Thank you for bringing this problem to my attention.