You could actually have the devices too close (overdriving the RF receiver). Or the two antennas are oriented with their null directions facing each other. My

You could actually have the devices too close (overdriving the RF receiver). Or the two antennas are oriented with their null directions facing each other. My go-to method to get difficult BT gear to pair is to place both devices in the microwave and shut the door. The microwave is a faraday cage for 2.4Ghz, so it removes interference as a potential problem. If it still fails, you can turn on the microwave and enjoy a light show at least.