I use NodeCanvas in my projects and I love it but recently I noticed a problem.
Since you keep some icon files in Design\Editor\Resources folders, these files end up in Game builds because Unity includes all assets in Resources folders without a reference check.
3rd party tools should not include a Resources folder for editor-only files such as UI icons.
Here is the screenshot of a built-assets analysis which shows that your editor related icons end up in the Game build.