So an app that uses an unofficial API broke when that API changed?

Not news nor "blocking".

What is an "official API"?

Honest question, because AFAIK there's no guarantee or (legal) requirement to support any API. Whether that's fully documented, has SDKs or whether it's something reversed-engineered doesn't matter WRT the support the company owning the API is supposed or required to give.

Or am I wrong there?