Huge hole in the navmesh

So I got this huge hole in my navmesh for no apparent reason.

It’s covered by the navmesh volume. And the slope angle is set to 50 degrees so it shouldn’t affect it.
I ahven’t added any volumes or actors that would cut the navmesh as far as I know as there is nothing visual that might cause the issue.

If I place a block over the area the navmesh generates as it should. It’s just the terrain in this particular rectangle.

Any ideas what might cause this?
I guess I have to regenerate the terrain, but I’m not sure how.

What happens if you delete the navmesh volume and add a new one (making sure the XYZ of the navmesh is enough to cover everything).

I’d advise making a backup of the level so you don’t loose anything.

Tried to delete the old navmesh volume and create a new one.
Also made the new one smaller, but still covering the entire area.

But no, hole is still there.

What happens if you move all things that are currently in that area of the Navmesh out of the Navmesh area. Maybe check if there’s something that’s been left underneath the landscape as well.

It might also be worth Googling about the error if you haven’t already.