There might be some more information you would want to give; like the bedroom may be right over an unheated garage. This means that the ductwork from the middle of the house has to heat an end room that has a much higher heat loss than other rooms.
When I first moved into my town as a heating contractor 30 years ago, I had a few years where I added duct booster fans and cut additional ducts into many of these end bedrooms to make them habitable. Usually it was the children's rooms.
The problem was that estimating air flow and calculating heat requirements for correct duct air flow requires math and is the most difficult design problem for contractors. They often goof on these end rooms by not putting enough ducts or large enough ducts for proper air flow.