mbrs unless you can prevent the banking app force restarting itself via the use of Battery Exception for example the only short term resolution I can see would be to place your SIM in another device while you receive the SMS OTP.
I understand what you mean in that the notification you get from the stock messaging app does not display a text preview but just informs you, you have a message. I haven't encountered this issue as I was able to use the multi tasking pane to swap in and out of Messaging without it closing on me.