This sounds like the situation at SIN. When you arrive, you are airside and can assess the transit hotel, but once you clear immigration and customs, you cannot get back to the transit hotel unless you have checked in for a flight departing from that part of the airport. If you don't check luggage, you can land, go to the transit hotel, and stay as long as you like and have reserved/paid for, but once you clear immigration to retrieve checked luggage, you are land side and cannot return airside without a boarding pass for a flight departing from that terminal.