This happens all the time by all the companies. They all operate at the direction of the forces in charge there. The forces can close the JSA on a whim for any kind of "training exercise" no matter how big or small. That's why it seems they just cancel them recklessly. They book them but they're never guaranteed. It's just how it works. If they do close it, you do get a refund. You don't have to take another tour.

Koridoor is considered the best - they're actually the "official" USO operator. Cosmojin is also popular.