With the main camera already plugged in, when I tap the Enter button on the ASIAIR app with cameras initially set to None, and only select a main camera after the ASIAIR app has fully launched and running, the square green fine-focus frame does not show up in the Focus window. The actual fine focus FOV that is used is apparently at the upper left corner of the image of the main focusing screen (which is not a great place to focus if the image plane is not perfectly flat and the target object is at the center of the chip).
However, if I first select a Main camera before I tap on the initial Enter button, the movable green square fine-focus frame shows up properly in the Focus window.
The behavior appears to be consistent across two different iPads (one is an iPad pro) running iOS 12.2. The ASIAIR app is Version 1.0.9, with Firmware 2.14 in the ASIAIR.
All in all, IMHO the ASIAIR is the best thing since sliced bread in terms of ease of use. A tip of the hat to ZWO.
Clear Skies,
Kok Chen