Sorry. I wish I could help you. The only things I can think of now are trying with a different Wi-fi connection with a different ISP.

You can also try removing all your repositories, then delete all other remaining items from "/var/lib/apt/lists/" and then add the repositories manually.

If you did a restore from a backup, that might be the reason why the problem reoccured after reflashing. As a last resort you can try reflashing again and do not restore the application list and settings.