Based on your description listed above and the defect shown I would suggest you check your nozzle heater bands and or thermocouple. It appears your injecting a cold slug of material because of the direct gating.There is no other place for the cold slug to go except for the surfaces of the part. All too the nozzle thermocouple is placed directly under a heater band causing the heats to appear to be up to temperature but actually be much lower.