There are some insanely good architects and programmers. Even so, people write mistaken code, design with faulty assumptions, misinterpret business logic, use libraries and crypto incorrectly, etc. On top of all that, there is a small segment of coders who insert malicious code. They used to write for mayhem but now more for profit.

The terms are somewhat contentious, but AIs are more prone to use heuristics than traditional algorithms, which would add another layer of complexity.

So, we can't be certain that such an AI itself wouldn't create bugs. If anything, it would be easier to show that bugs would get created.

This is simply the state of software. We all deal with it in the ways we can, trying our best to minimize issues and add value.

Strong AI wouldn't be enough, if by strong AI you mean "enough to pass the Turing test". Humans pass the Turing test all the time, but still produce buggy software.