Diagnosis
The Air Pro does not have a persistent auto-resume function after a total power loss. It defaults to an off state.
How to Fix It
You must manually press the physical power button on the unit after power is restored. It will not restart via the app if the unit is in an off state.
If That Didn't Work
If the unit still does not power on, perform a hard reset. Unplug it from the wall. Hold the power button on the front for 30 seconds. Release. Plug it back in and press power once.
Heads Up
For automatic operation after outages, you would need to plug the purifier into a smart plug and configure the smart plug to restore power, not the purifier itself.