What are likely causes of mild/moderate knee/lower leg pain only present when running, no swell/tenderness, pain changes spots, pain stops after run?

Shin splints likely: Make sure you are wearing a reasonable running shoe that fits well. A sudden increase in distance and/or running intensity can harken shin splints which is really just an overuse injury. The treatment is to decrease your intensity/distance akin to a dimmer switch to just below the threshold where symptoms develop. If pain persists for much longer, seek an orthopaedic evaluation.