My last Setter, Molly, was a bird machine. Her off days were times when she hunted for herself and got a bit out of control. Next day she would be a dream to hunt behind.
My current Setter, Major, quit on me during a cold snowy hunt in December. He seemed to not like the situation with two other dogs from the moment we put him in the truck kennel to drive from the house. It took encouraging to get him to hunt where usually he's quivering with excitement to be released. Really messed with my mind that this usually eager hunter was hesitant. One thing about the long haired dogs is the ice that builds up on the hair between their toes. After about 45 minutes, a couple good points and retrieve, no amount of helping him clear his paws would get him to go and he shut down.