WinSCP hang on startup when in VPN

I can reproduce this error with version 5.9 and 5.11

When I'm logged in a VPN that prevents internet access, winSCP will not startup.
I can "start" multiple winscp instances but no UI will be visible until I disconnect from the VPN.

The VPN client is "Cisco VPN client" 5.0.07.0440

OP here, I forgot to say that I'm on Windows 8.1 and that "winscp.exe /log=log.txt" does not produce any log.

Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.