It is possible that the receptacle was at one time half switched. If someone replaced it and did not cut the tab between the hot screws the switch function would not work. It is possible that more than one receptacle was switched. If any one of them was replaced and the tab not cut, all of them would become unswitched.
The first thing to do is to check the wiring at the receptacles.
The first thing to do is to check the wiring at the receptacles.