Not quite, since my player controller is using the navmesh itself. However, thank you for putting me on the right track; the navmodifier volume is not a scene component, so putting it on my actor did the job but the null area didn’t move with the player.
But poking around for that led me to this post by Epic’s AI designer, that navmodifier volumes shouldn’t be used for this purpose, but instead the “can affect navigation” setting for actors and setting the capsule component to navNull to create a moving non-pathing zone around the player actor. This worked well but since the player actor uses the navmesh for navigation, this led to some extremely bizarre behavior. So I went looking for ways to create a navmodifier that only applied to specific actors.
I couldn’t find anything like that, but I did find this post about nav filters. It’s not particularly elegant, since the filters only apply on a per-blueprint-block basis, but I set up a query to exclude a custom navmesh class I created (and set my player actor to), then added the query as a filter to my AI Move To Location block. That did it!