sounds like they need to be swapped.
Did you have the pet versions for any reason? Pet versions are a lot slower for obvious reasons
Also what size rooms are they in. A sensor is designed to detect 2 steps accross the detector. They are slower directly towards them etc, that is why placement is important.
Also you say the room is hot, how hot? you are right that sensors do struggle as the room approaches body temprature.
Its difficult for us to know how your testing etc, but if you are sure they are faulty then we will swap them, however we will test them on return for a fault.