How did you come to the conclusion they are partners? I've never seen any financial news that Apple became a partner with BoA. If you buy lettuce at your grocery store that was contaminated with E Coli at the source is the store a partner too?
I'm sure Apple would be more than happy to provide assistance to BoA, or the contractor they use to develop their app, if they were asked. But since the app does open, goes to the spinning cog showing it is attempting to connect with the BoA server, and then crashes out when it cannot, this is on BoA. It really doesn't surprise me, I had a past problem with them where they claimed the problem was with Safari, then it was any browser because I was on a Mac, then was Internet Explorer on a PC, then Chrome and Firefox on a PC, then Windows 8 and finally Windows 10. And somehow it turned out to be BoA.
If BoA gives Apple complete unrestricted access to their servers I'm sure Apple could help them. I also thing that will never happen.