We can confirm a reported DNS leak issue on Android that impacts all VPN apps. There are no known solutions to prevent it, and requires a fix in a future Android version. Details in our blog post: 
Depending on your threat model, consider avoiding the use of Android in situations where such leaks can impact your privacy.
IVPN
DNS traffic leak outside VPN tunnel on Android
Recently we were made aware of a potential DNS traffic leak outside the VPN tunnel on Android. Even with Android OS “Always-on VPN” and...