But the fact that many of us experience no problems with banking apps and betas suggests to me that the banks with problems are doing something in their code that isn't fully to API and other APPL standards. Otherwise, every banking app would have issues.
Actually, for earlier iOS releases, up until about iOS 11/12, all of them had issues, But then they changed, and now it’s a handful of banks using something the others are not. They could be using an API that the others have moved away from, that Apple breaks in the early betas and then fix. For instance, up until iOS 12, Barclays and Capital One would break, then work the same time as HSBC with a new Beta, but since then, those 2 don’t have the same issues with a new beta, but HSBC still does.
Pokémon Go suffered the same issue, but they’ve obviously changed whatever it was after they got hounded throughout the beta period the other year.
Not all banking apps are using the same code.