Best advice - if you have a friend or family who has the ability to block ports - temporarily use their network so you can update the security certificate of your hub. While using that instance of leaving Ethernet disconnected - I recommend leaving Ethernet connected.
For v2 hub:
remove batteries
Leave Ethernet cable connected between hub and network.
Block port 123 udp
Remove power cord
Press reset slow and insert power cord.
Continue holding for 30 seconds until you see solid yellow and release
Onboard hub into app
if you see a file downloading, remove the block of the port
If it has a really old firmware version, be patient, it can take time as it needs to apply every single firmware version.
More details on how others were able to resolve the issue