Its a not a jj thing, its a cell thing. JJs read a cell same as any other rebreather on the planet. Your cell goes 9-40mv, thats 31mv to 1.0 PPO. My cells new are 10.7 - 50mv, thats 40MV. Thats almost 25% less range you have alone from .21 - 1.0. Your cell reads 40mv at 1.0, mine read 50, thats 20% less than a new cell.
Theres no such thing as cell "wake up", but there is such a thing as cell failure. One of the big symptoms for me is low output at 1.0, coupled with yours acting up, screams a cell issue.
Have you spiked that cell to 1.6 during a dive and verified its not voltage limited? (or current limited, depending on your religion)?