Sounds like you are in the industry, and we all know sometimes it doesn't always go as planned. I spent the last 20 years of my career working in the high-availability backend IT environment, and even the best companies had an occasional "oops" release/update, and our customers were banks, credit card companies, global services companies, etc. I can easily imagine a relatively small company such as HGV doesn't have near the rigorous IT processes and QA as the companies I worked with.
In order to do comprehensive QA testing, you generally need environments (HW and SW) that replicates and emulates the actual production environment. That is not a simple environment to set up, and many times there are small differences between the QA environments and the production environments. Most of the time those small differences don't matter, but every once in a while an update may work fine in the QA environment but blows up in production. It happens.
Kurt