Oceania, at the end of the game, there’s a bug, can you help?

So, I spent a very long time playing the "Oceania" map (not WOG, just the regular Heroes of Might and Magic III: The Shadow of Death), and I finally defeated almost everyone. In the end, one computer-controlled player hid in a closed-off area in the upper right corner, and the only way to get there is by bringing the "Sphere of Permanence" artifact. I control the entire map, but this artifact is nowhere to be found. What should I do?