There are many routes, but in your example, for instance, Microsoft updates don’t just have 1 fix for 1 issue but multiple fixes and new features, ideally Microsoft would have tests that cover all usages that they run before deployment, but they don’t (it’s a lot of code) but also it has to run on any combination of systems.

Then you throw vibe coding into the mix…

Another thing is if you had 2 similarly named variables and use the wrong one it might work one way but not another, someone is tasked to fix it and they see it using the wrong variable and correct it… great, but maybe other stuff was made since that now breaks because that variable is correct now.

And any issue relating to timing issues can just appear and disappear based on environmental conditions, a true nightmare to resolve well.