It’s possible the hog is in the hog house, hibernating. The males tend to start hibernation much earlier than the females. Although it could have been practising and have gone elsewhere to built an actual hibernation nest. If it was making the nest over several days, it seems less likely it was a birthing nest.
If you are continuing leaving food and water out, it’s best not to leave it too close to a nesting box in case it attracts predators.
I would check the area to be cleared very carefully just before any work starts. If it’s the sort of area hogs like, there could easily be more. But also if the hog is hibernating in the box, they do sometimes make another new nest during the hibernation period.
Good luck. Hope all goes well.