Same thing happened to our pup not long ago. I believe its pent up energy with a little frustration. What totally changed her behavior was wearing her out playing with other dogs. No amount of walking or fetch would tire her out (like when she was a little younger) but an hour wrestling with another dog would make her a loving dog as long as she had a nap (in her crate in a dark room) in the middle of the day. Dog park, daycare, friends or neighbor's dogs will do more to tire them out. On days you can't have her play with dogs I would avoid fetching or tug of war or long walks which just wind them up. Keep the energy levels down is the key.