I was facing a similar problem. I have my own OpenVPN server on an Asus RT-AC66UB1. The server was set and configured using the Asus built in tool. The OpenVPN client file was installed in the AR300M. During quite some time I could connect to the VPN server without any problem and to surf through the web flawlessly, but since some time ago I was facing problems to access most of the websites and servers, but the connection to my OpenVPN server has been always established. While reading your posts I managed to understand that the problem might be coming from a DNS resolving issue, therefore I made this setting:

By doing this, my problems disappeared. This applies to the AR300M with 3.215 firmware as well as for the Mudi E750 with 3.215 firmware.
I hope this helps.

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