Wrong identification of pawn
Navigation volume is built correctly. However, pawn is wrongly cognised so the immediate path cannot be found.

There should be robust way to find the pawn. More importantly, for Find Path Immediately the pawn is not necessary - it is ultimately to find a path between just two points.
Also, why does FindVolume need to be called over and over again? Navigation volume is an object persisting to scene and once found needed just be retained.
Here might be the problem: GetOwner() in USVONNavigationComponent::HasNavData() returns sometimes AIController and sometimes the pawn. The two are located in different locations (in my case). The wrong owner gets taken and then causes above error. The right owner should be the pawn. AIController is just the component - does not own anything.
This double owning exists even without call to Find Immediate Path, though the error in red in the above screenshot is emitted by Find Immediate Path.
Immediate fix is to get actor location from pawn in USVONNavigationComponent::GetPawnPosition() if casting to AController fails.
My experience, however, points out that "true" fix would be to resolve double owning, at app architectural level.
Does author prefer that I make a pull request with this immediate fix?