Why the nRF52 DK and nRF9160 DK are not connecting via Bluetooth?

[ntnudokka]

We have bought one nRF52 DK and one nRF9160 DK with proper programming (the nRF9160 is able to connect to the cloud via cellular network), but the two devices are not able to connect via bluetooth, May we know why?

[awneil]

So what firmware do you have running on the two kits?

What debugging have you done to find what's going on?