Try rebooting your router, and log out of your mydlink account and back in.
Since the portal and the app are showing them offline, there is some break in communication between the cameras and the mydlink server.
The cameras use the DNS server address so on 1 of the cameras change the DNS server to something else - 4.4.2.2, 8.8.8.8, 1.1.1.1, etc and see if that works.