It seems a bit strange that the box has never been unoccupied in 6 years. Hogs normally change nests from time to time, not least to minimise problems from external parasites. Do you have a camera which checks whether the box is occupied?
It is normally recommended to clean out the boxes in the Spring and Autumn. Here is a link
But really if there is a time when you are sure that the box isn’t occupied – by which I mean, not just that the inhabitants have gone out for the night, but if no-one is in residence at all, in the daytime either.
If you do get a chance to clean it out, you could put a small amount of fresh bedding in, but many hogs prefer to take in their own bedding and arrange it to their satisfaction, so you may like to leave a pile of suitable material nearby. i.e. leaves, long grasses, hay, etc.