NavMeshAgent occasionally makes stale paths

I'm working on an AI that needs to be able to investigate by walking between arbitrary points on the navmesh. However, sometimes it stops for no apparent reason. When this happens the isPathStale returns true, pathPending returns true and pathStatus fluctuates between PathComplete and PathPartial on my NavMeshAgent.

I've tried using ResetPath and SetDestination again to try to make it continue moving, but this produces the same results.

Mostly there's no problem, it only happens occasionally, but it always fails between the same origin and target points.

I have no idea how to fix this, or even circumvent the problem. Any ideas?

Edit: When the problem occurs, it occurs to all navmeshagents at the same time.