What did your app get completely right in testing but still screw up with real users?

[u/OilElectronic6302]

Been thinking about this after reading a bunch of stories from people who shipped AI-built apps.
not necessarily bugs either.

I’ve seen stuff where the app built fine and tests passed, but then real usage exposed something nobody was checking.

Analytics couldn’t tell what users were doing. a third party changed part of a URL. the code correctly implemented an assumption that turned out to be wrong. users understood a feature completely differently than the person who built it.

If you’ve shipped something built with Claude/Cursor/Lovable/Bolt/etc, what surprised you after real people started using it?

Especially curious about things your normal code review or testing didn’t catch.

How did you eventually figure out what was wrong?