Has an API ever silently changed its response shape and broken your app before you noticed?

I keep running into (and hearing about) a specific kind of bug that never throws an error — an API you depend on quietly changes its response shape. A field disappears. A number becomes a string. Something that was always present is suddenly null. Nothing crashes immediately. It just produces wrong or missing data somewhere downstream, and you find out from a bug report, not a log. I'm curious how common this actually is outside my own experience, so — genuine question, not a pitch: Has this happened to you, with a third-party API or even an internal one your own team owns? How did you find out it happened — a user report, a stack trace somewhere unrelated, manual debugging? Do you currently do anything to catch this kind of thing before it bites you (contract tests, monitoring, or just... hoping)? If you don't do anything about it today, is that because it's not painful enough to bother, or because you just haven't found a lightweight way to? Not selling anything here, just trying to understand how real and how painful this actually is for people building on top of APIs day to day. Would genuinely appreciate hearing your experience, even a one-line "yeah this happened to me once, wasn't a big deal" is useful data.