OpenVPN connection is successfully established and I can PING my sandbox via hostname, but I cannot open OSA Panel via port 8080. SSH and FTP also do not work.
Moreover - PING to the sandbox returns IP from the 199.x range, but it should be 10.x range.
It is caused by the manner how Windows works with OpenVPN.
When OpenVPN client creates VPN connection - it offers Windows to use suggested DNS in order to handle all corresponding requests via this DNS server.
However, in the latest updates of Windows 8/10 such behavior is changed and, as a result, Windows rejects DNS server offered by OpenVPN (sometimes or every time) and proceeds using Primary DNS servers of current Internet connection.
So requests sent to the apsdemo.org network cannot be correctly resolved.
The easiest and the fastest way to workaround such Winows<->OpenVPN interaction is defining Primary DNS server manually in the connection settings.
Please set manually this DNS server IP: 10.112.0.11 (points to the dns.apsdemo.org)
There is an example how to configure it for the Windows 8/10:
Also, it might be beneficial to disable IPv6 on VPN or all network interfaces if you still cannot connect.