When connecting to an OpenVPN endpoint, you will be able to access resources on the networks that the OpenVPN server publishes routes to. Other traffic however, such as to the Internet, might still route via your local network and not out using OpenVPN to the remote network first. This can cause some websites to be inaccessible, such as attempting to read local news or watch online TV streaming services while abroad, or may pose a potential security risk, if for example you're connected to an open wireless network in a hotel or a coffee shop.
To fix this, add the following line to the OVPN configuration file for the connection you are using, disconnect and reconnect.
Once you reconnect, the remote OpenVPN server will now be used as your default gateway and all Internet traffic will be routed over the VPN tunnel.