Using Keynote Remote between iPhone and iPad

Hi. My issue is a bit quirky. I have two iPhones (7 and 7 Plus) and two iPads (Air and Air 2) all running iOS 11.2.6. Keynote is up to date on all devices.

Here’s the thing. I can use the iPhone 7 to control Keynote on the both iPads. I can use the iPads to control Keynote on each other. I can use the 7 Plus to control the other iPhone and the Air 2. I can use the two iPads to control Keynote on the 7. But, for some reason, the Air and the 7 Plus will not talk to each other. I’ve turned both Bluetooth and WiFi off and back on, on all devices. I’ve force restarted all devices. I’ve force quit Keynote of all devices. Any ideas?