It may have been the weather or more importantly the temperature.
Alkaline batteries really do not like the cold and give out much lower voltages than in warmer temperatures.
As the Rotor runs of fewer batteries it would have an adverse effect to the power running the loader.
I had trouble at an event last year which was sorted by either swapping for a fresh set of batteries that had been in the car or keeping the marker etc in the car between games.
Laters