Google's DNS services worldwide have updated the correct DNS records and all FLOW portal URLs are available again.
The cause has been identified as a communication error between our DNS provider and the Google Global DNS servers which caused corrupted DNS records on Google's side.
In case you still have connection problems then we advise you to clear your machine's DNS cache. Detailed instructions can be found on this site: https://www.whatsmydns.net/flush-dns.html
We sincerely apologize for any inconvenience this may have caused.