I always think it's important to practice dog training in a variety of different locations. If only ever practice it at home, your dog will only ever know it at home. Make it easy for them, take breaks and if they struggle, then go back a stage.
If training a dog that might be more sensitive to sitting on a cold floor or hard floor, then it is important to consider this when training. If you ask a dog that has arthritis to sit down, on a hard floor, this might be the reason he is 'refusing' to sit. So don't force him, it isn't worth damaging your relationship and making him feel anxious.
If he normally responds to a cue, then for some reason he stops, perhaps get him checked at the vets and consider the surroundings. A good way to think, if you had to do what was being asked of him, would you do it? If you wouldn't sit on a cold, hard floor with bad hips, then don't expect your dog too.
Training should be just as fun for your dog, as it is for you.