Being that it is such a popular show, isn't it possible that it's just sold out?
If not, I'd vote for maintenance or theater refurb/upgrades. January is a slow month for tourism, usually one water park or the other is closed then, too, I believe. If they needed to close down to do any work on the venue, that'd be the month to do it. Besides, it might not even be that it's closed for a month, it might only be closed for a week, but it happens to coincide with the week you are going. Small consolation if you really want to see the show, but no reason for anyone to read anything ominous into it. I say use that money to have 2 character dinners.