I get this from time to time, and there’s never any means to actually verify the connection. It’s a total dead end. It seems to often happen when working on a theme that frequently gets 429 errors due to an errant app messing with the fetch prototype and getting stuck in a loop.
It’s usually when I’m working without being connected to a VPN. If I connect to a VPN (using Mullvad, fwiw) then the need to verify goes away, which strikes me as a bit ironic, but just sharing that here incase it helps anyone else.