Cannot obtain IP if the screen is off. (Android 5.1.1)

[biheex]

The app is working as expected as a vpn repeater, but when the device screen is off, other devices fail to obtain IP addresses even though the "DHCP workaround" is enabled.

Device: Samsung SM-J200F (j2)
Android 5.1.1 [rooted]
App version: 2.15.2

The moment I open the app or just turn on the screen, at that moment other devices obtain the IP successfully.

How can we connect and obtain the IP while the phone is idle (screen is off)

[biheex]

[solved] I set up static IPs on recipient devices.