I called up SingTel, the rep has been understanding and says this requires surfacing to backend to investigate. Meaning, it will take time to resolve for those of us who do not have immediate access to a VPN.

In the end, I went ahead to get a paid 1-month VPN service... This got me past the launcher checker and into the game. Unfortunately, this is the immediate solution to the log-in issue until the ISP resolves this on their end.