Correct me if I'm wrong, but I think S3a stage is determined by the engine temperature. I've also made the similar observation recently after a couple of months of "feathering" the pedal. This week I find myself having difficulty shutting of the ICE when driving less than 40mph. I've never had this problem in the past while driving in the same LA traffic. Only difference I've noticed is the temperature here in LA has suddenly dropped into the 60's and low 70's this past week (as opposed to 90's and 100's just few weeks ago). I guess with the cooler weather, if I cruise around in EV mode too long the engine temperature will cool down and enter into S3a stage even if I've been on the road for over 30 min. Does this make sense?