Why does the Internet stop working when connecting to OpenVPN on an Android smartphone?

Question

Android

OpenVPN has been deployed on the server and most Android smartphones successfully connect to it. At the same time, the Internet stops working on the smartphone. Only the server itself is pinged. But, strangely, on the old Lenovo A789 with Android 4.0.4 everything is in order: both the server pings and the Internet works. What is the problem? Maybe on new smartphones there are some settings that block the Internet during a VPN connection?