I was having the same issue after turning on NAV mesh invokers. You kind of just have to trust that it’s working at this point because it’s not actually going to build your nav mesh unless there’s an Evoker present. Which is usually placed on your AI and your player. Just make sure the volume encompasses your whole level and you’ll be fine.
But if you want to see it again in the viewport, you need to disable invokers set your nav mash generation back to static, then cut and paste your nav mesh volume and it should generate again.