It sounds like a confidence issue thats all...................It may sound stupid but worth a try but Tie a rabbit skin to a length of baling cord and then to a long hazel pole. Ask a friend to pop over when it's dark and hold the lamp on the skin while you move it about then slip the dog( only a few yards away) . Let the dog mouth the skin with plenty off praise ..................... don't let the dog get to hard mouth with it keep the session pretty short repeat a few times then take the dog out on the lamp.
Don't panic thou mate day time bunnies are much harder than night timers so you