Wells Fargo has a very long and well-established history of making "mistakes" in their own favor that harm their customers and/or break laws. These "mistakes" are typically non-technical in nature, have nothing to do with engineering standards, and in several cases appear to be a matter of deliberate bank policy:
> On February 2, 2018, the U.S. Federal Reserve Bank barred Wells Fargo from growing its asset base any further, based upon years of misconduct, until Wells Fargo fixes its internal problems to the satisfaction of the Federal Reserve. In April 2018, The Wall Street Journal reported that the United States Department of Labor had launched a probe into whether Wells Fargo was pushing its customers into more expensive retirement plans as well as into retirement funds managed by Wells Fargo itself. Subsequently in May 2018, The Wall Street Journal reported that Wells Fargo's business banking group had improperly altered documents about business clients in 2017 and early 2018.
https://en.wikipedia.org/wiki/Wells_Fargo
These are just from the past couple of years. Check out their Wikipedia page for many, many more. This isn't even the first time they made serious "mistakes" with mortgages specifically: check out their 2012 settlement. Here's the judgement in just one case:
> On April 5, 2012, a federal judge ordered Wells Fargo to pay $3.1 million in punitive damages over a single loan, one of the largest fines for a bank ever for mortgaging service misconduct. Elizabeth Magner, a federal bankruptcy judge in the Eastern District of Louisiana, cited the bank's behavior as "highly reprehensible", stating that Wells Fargo has taken advantage of borrowers who rely on the bank's accurate calculations. She went on to add, "perhaps more disturbing is Wells Fargo's refusal to voluntarily correct its errors. It prefers to rely on the ignorance of borrowers or their inability to fund a challenge to its demands, rather than voluntarily relinquish gains obtained through improper accounting methods."
Blaming the programmers for these "mistakes" is like blaming bank tellers for the reckless banking policies that caused the 2008 meltdown.
This has nothing to do with "engineering standards". Notice that all these "mistakes" benefit Wells Fargo at the expense of its customers and/or the law. If it was just "shoddy standards", you'd expect a few mistakes to be in favor of the customers...
These "mistakes" proliferate because they make the bank money, and only cost them a slap on the wrist and some small fines. This is Too Big to Fail in action.