When I run the wikitude app (I got it from play store) the radar works fine; I am able to see different POIs when I turn around the phone and the north indicator changes accordingly.
I read in this forum that you recommended to downgrade sdk to version 6 to someone else who had similar problems, nevertheless, I couldn't find that version in downloads section.
You're right, with 7.1 is working fine now.
it seems like you are using Wikitude SDK 7.0 and not 7.1. In 7.0 there was an issue with POIs when the device did not have a Gyroscope which is true for the Galaxy Grand Prime.
It is working on the Wikitude App since it was using SDK 6.1 until today.
Please make sure that you are using 7.1. as this should fix the issue.