This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
If a Blueprint is derived from NavLinkProxy, and then that Blueprint is added to another Blueprint as a ChildActorComponent, the second Blueprint's Smart Link functionality will not work when the project is opened in the Editor until the nav paths are rebuilt. Nav paths have to be rebuilt every time the Editor is opened.
EDIT: I was unable to test this in 4.8 or Main because the included SmartLinkComponent does not appear to be creating the Box Obstacle it was asked to create (reported in [Link Removed]).
The nav path past the second obstacle is no longer drawn.
A nav path past both obstacles is still drawn.
Head over to the existing Questions & Answers thread and let us know what's up.