I just fixed this issue.
I got the procedure from Superuser @plemans by using a Google search.
Note: the procedure uses the word "router" but means "extender" in most places and the Ethernet cable needs to run from the computer to the extender. Connect it at the bottom of the extender and then plug the extender into the wall. The actual router needs to be unplugged, while all other ethernet cables in the house need to be removed from the wall at that step of the procedure. Lastly, be sure the firmware file is saved to the desktop (regardless of where the folder or compressed zip folder are saved) and the file extension is .img in the command prompt. If you type -1 instead of -i in the suggested command prompt, you will receive an explanation of what each part of the suggested command prompt means.
Usually if its blinking green, something went wrong during the update and its stuck. You can force install the firmware to the device. Any time you do an update I recommend doing it over a hardwired connection. I know the option is there to auto update but most of the problems happen from that features. To force the firmware to it, you have to use a tftp procedure.
https://kb.netgear.com/000059634/How-to-upload-firmware-to-a-NETGEAR-router-using-Windows-TFTP
also make sure to enable tftp from within windows 10 (if thats what you're using)
https://www.thewindowsclub.com/enable-tftp-windows-10
