My best guess is that there is a room available between 1/20 and 1/23 that is already reserved from 1/24 until some other date, and a different room available from 1/23 to 1/27 that someone else has from some earlier date to 1/23.
Dumb Disney booking algorithm working against you. Must make sense for the computers somewhere behind the scenes (likely caused by programming designed to minimize orphan rooms). I’d suggest calling the main reservation line and working through it with them. They’ll probably have to pull in guest services.