If the hedgehog has been visiting since March, it would have come out of hibernation then. They don’t normally stay in their hibernation nests for any length of time. They apparently even sometimes change nests in the middle of hibernation. But if they stay too long, the nest is likely to become a good place for parasites.
So it may be that the hog was finding too many unwanted visitors in the nest, so decided it was time to move. But, if that was the case, it would be likely to still visit for food.
The male hedgehogs normally come out of hibernation earlier than the females. Coming out of hibernation in March, suggests a male, to me. Male hedgehogs have a larger range than females, so it is less likely that they will visit any one part of that range every night. However, if it was a young male hedgehog, it’s possible he is exploring further afield, and may even move to an area further away, most, if not all of the time. That is the sort of pattern I have observed here, with the young males gradually visiting less and less frequently. So it may be a case of him being grown up and leaving home.
Try leaving something across the front of the hog house for a few days to make sure there is no-one coming or going, and if you are sure that there is no hog in residence, it might be a good chance to give the hog house a clean out. Don’t use chemicals, but use boiling water so that any parasite eggs in the cracks are killed. Then hopefully you may get a new tenant. For more information about cleaning hog houses, please see:
Good luck. I hope you get a hog using your box again soon.