Is it specific to your bank? I have used a couple of the big name American bank apps on my phone and never seen a dialog whatsoever (the blue and the red bank just FYI). Or it could be specific to your setup. Are you using Microg and hiding root (if you have it)? Are you making sure that all of the microg checks pass? Does the microg signature spoof pass?

Perhaps as a last resort, after getting your install set up, close the bootloader again. I don't do that but I've heard of people having trouble from leaving the bootloader unlocked.