Heat loss - hot spots on roof
All homes have variation in heat loss. Yours seems to correspond with the soffit vents. It could just be that the additional airflow in that area leads to more melting in marginally cold weather. It doesn't take much heat to melt snow on a 35 degree day. 

It could also be that there's another vent directed through the soffit vent. It's all guesswork until you inspect the attic, but I see no reason to be alarmed.