I know it is worrying when they disappear for a while, but it is not unusual. They do apparently sometimes even move to a different nest, during hibernation.
I would have suggested giving the box a quick clean out while he/she is away if he/she has been using it for a long time ( I usually use boiling water to hopefully try to get rid of any unwanted visitors’ eggs in the box – rather than any chemicals, which might be bad for the hog), but having heard from someone else that a hog had recently produced hoglets already, you would need to be very careful in case it is a female with hoglets. Although, she would not have left them that long – but cameras can sometimes miss hogs, I find. They have been known to eat very small babies if they are disturbed at the wrong time, so it is not worth taking the risk. I would keep an eye on the box and only consider cleaning it out if no-one visits for several days. Maybe put a little bit of bedding in and a bit more outside, like you did before. It is getting a bit late to do it, but if you are absolutely certain it is no longer in use, should still be ok if it is not being used.
It is not a good idea, if a hog is actually in residence, to take it out to clean the box.
Hope Ralph (not sure what the female version of that is!) reappears soon.