I'm in the same boat as you - was on KE26 in early December. Looks like Korean Air pulled that flight from the schedule after September, presumably to use that aircraft to fly other routes that are now resuming. Even after January now, the KE26 is no longer scheduled except for a few days in January around the return from winter break. They sent me an email earlier today about KE26 being cancelled and being automatically rebooked to KE24. They are allowing a one time change to any date/routing I want on the website, although I booked directly with KE using miles. If you booked direct with them, contact KE customer service if you didn't get the email yet.