I am sorry for the late reply due to summer vacation!
Just to clarify, are you trying to update an existing project FROM version 5.3.x or 5.4.x and TO 5.5.x+ , which already has work done with a NodeCanvas version prior to NC v2.6 ?
Does the Unity console reads any errors before or after (next restart) of the the crash?
What are the contents of the .unitypackage you are importing?