Basically, there are three possible reasons why your Linksys AC1200 extender is blinking green. This mostly blinks when the AC1200 extender boots up for the first time after being plugged into a power outlet. The other scenario is while you are updating the firmware on the extender; in such an instance, the green light will flash to indicate that the process is ongoing. In addition, if you are resetting the extender due to performance or other problems, the same LED will be seen on the panel. It will, however, transform into a different light once you reset it completely and perform the Linksys ac1200 setup. Lastly, after you finish configuring the extender using the WPS method, you may notice a green light on the device. This means there will be no need to worry about the blinking green LED on the extender as there is a process that is in progress. Which shows that the extender is performing a process successfully or without any glitches.