I would recommend powering the amp on first, ensure that it is connected in Bluetooth settings, maybe playback some music or something to confirm, then launching the app. That way when the app is launching it already knows the amp is there (should reconnect automatically over Bluetooth) and can begin it's data connection for loading tones and whatnot.
Without going into too much detail... there are two protocols to Bluetooth, one which carries audio, and the other which carries data. AMPLIFi Remote uses both, and even though the audio may work, the data connection may close when an error occurs (likely between firmware updates). The best way to re-establish data connection is to break down the bluetooth connection entirely and pair it again. After that, it should remain stable and reconnect accordingly. Once again, stay tuned for the firmware update that is coming soon, it fixes a root cause which shuts down the data connection, but leaves the audio connection, which is the part that is deceiving.