Navigation/pathfinding doesn't work when FPS < 20

I’m developing a first-person mobile game with controls very similar to Epic Citadel. If I tap to move while the framerate happens to be below 20FPS, the touch input is registered and my navigation marker appears, but the pathfinding (called via GetWorld()->GetNavigationSystem()->SimpleMoveToLocation()) doesn’t work. If the framerate lifts even a fraction above 20, the move works fine.

Is there a checkbox I’m missing somewhere that disables navigation at low framerates, or is this a bug? Obviously I’ll be doing everything I can to ensure the framerate doesn’t dip that low, but in the case where that fails, not being able to move is a critical issue.

Epic, can I get some help on this issue? It’s going to make the game literally unplayable for anyone with a low-end device.