I just tried to replicate this with the latest version of NodeCanvas from asset store and Unity 2022.1.19f1, but there were no errors poping up. Just to clarify, here is what I tried:
1) I made a simple custom Action Task with a public Timeline Asset type field and added that action task in a graph.
2) I also assigned a Timeline Asset I had created there.
3) I opened up Unity’s Timeline Editor and selected various clips that I created within that Timeline.
Can you please let me know any way for reproducing the errors you see poping up?