Hmm . . . That is odd. I wonder if the messages that are being displayed are misleading you?
Start by disconnecting the Ethernet patch lead and then power-cycle the HG612. Leave the HG612 alone for a few minutes, then press the reset button and hold it for 15 - 20 seconds. Once you have released the reset button, allow the device to remain powered up for, say, five minutes.
Power off the HG612 and reconnect the Ethernet patch cable to the LAN2 port. With the reset button held depressed, power on the HG612. Continue to keep the reset button depressed. After 20 - 30 seconds, release the button and then point your web-browser to the 192.168.1.1 IPv4 address.
The firmware upload page should now be displayed. Specify the the firmware image and and left-click on the upload button. At this point, do not disturb the HG612 or your computer. Ignore any messages that are subsequently displayed that the page at IPv4 192.168.1.1 cannot be reached. They are originating from your web-browser and can be disregarded. It is very important not to disturb the HG612 at this point, for it will be checking the image that has just been uploaded. I will suggest waiting, once again, for five minutes. During that time, if you are keeping a close watch on the LEDs, you will see that the HG612 re-boots itself. Once it has re-stabilised, it will then be using the newly uploaded firmware image.
It is important to allow the device time to perform its internal housekeeping tasks . . . if it is interrupted, the uploaded firmware will be deleted. Hence the advice is to wait up to five minutes at each crucial point.