CM500-100NAS ethernet led light is amber

model is CM500, light all green when with old wifi router. After changing the wifi router to R6120, CM500 model ethernet led turn to amber. If connect to the old wifi router again, CM500 model ethernet led turn to green. 

rebooted CM500 and R6120, CM500 model ethernet led still is Amber.

internet connection is good, but internet speed is slow.