I had same issue while using Samsung A40 (no issue with iPad Air before). I solved it like this
- first, i did the last firmware update (i don’t know if it is part of the cure but anyway i did it).
- I registered the Magene as Power Source with Bluetooth (not Ant).
- Then i clicked on “Controllable”, and it was there.
the conclusion is that Controllable is only available and discoverable in Bluetooth not Ant