Hello,

The first time the nodes are loaded when you right click in the canvas, the node documentation for Unity classes is being cached. After this is done once it will be fast until entering/exiting playmode, at which point they will be re-cached.
If you want, you can turn the “Show Help” off in the Prefs at the top of the editor window, to disable the documentation and as such be no need to load them.

Let me know.