Azure VPN (basic) P2S won't connect using IKEv2

I have an Azure VPN (Basic SKU) that has been working fine using SSTP for Point-to-site connections. I tried following the steps in migrate your VPN gateway (Option 1) to migrate to IKEv2. However, the new VPN client never connects - it just sits at "Verifying the password" and counts seconds forever (or "Connecting to ..." if I use the powershell client installer). If I re-install the old client, it connects just fine again using SSTP (NOTE: this is with no other change to the Virtual network gateway itself). I've tried disabling the Firewall on my Windows machine and on my router, but no change.