I agree that it's hard to see from the outside how calculating weight figures for an airplane could be software load-dependent. But this all smacks of the point that Brooks makes in 'The Mythical Man Month' all those years ago. Two guys in a garage can make a program that does 'x', but to make a programming system product that does 'x' is more than an order of magnitude more work. The complexities introduced don't relate to the 'x', but the intricacies of large systems. Deciding that 'someone has fucked up and should never work again'? Sorry, competent and conscientious people regularly make such mistakes. Which is why we need tests, software review, engineering processes et al to catch those mistakes.

Boeing itself (unsure about this company though) was widely reported to have offshored their senior engineers a few years ago. eg:

https://www.bloomberg.com/news/articles/2019-06-28/boeing-s-... (paywalled)

https://archive.is/vdg9S (paywall workaround)

Note that there were several articles about it around the time, the above one is just the first reasonable seeming one from a quick search.

I can give you a simple example on how this can happen, from a real production system in a different regulated environment: all the SQL SELECT statements are WITH (NOLOCK) on MS SQL server, resulting in non-committed (dirty) reads. Under very light load it works fine, on higher loads it reads some dirty data. If you calculate the weight of the plane by adding the weight of the checked in luggage plus passengers read from a shared database, some differences will appear and they will increase with the load as more transactions will be in flight and possibly read or ignored.