Ask HN: How do you detect silent data loss in user-facing systems?

Some web analytics libraries will take screen recordings of each user session. (No comment on the ethics of that.) Making a habit of watching those recordings in the early days of releasing a new feature or major UX change is a common pattern for detecting when users give up and supporting theories as to why.

I have seen many websites that detect if you've entered something into a field or touched some control and then try to switch away from the page. They then pop up a dialog box saying something like "you have unsaved changes, are you sure you want to leave?"