I think this has noting to do with date-fns. I could reproduce the behavior within the interactive code example in React Native's "get started" page just using a native Date object. Works on web, breaks on iOS.

The problem is that you are using a string in the Date constructor, which can behave differently depending on the runtime.

Per MDN:

Note: Parsing of date strings with the Date constructor (and Date.parse(), which works the same way) is strongly discouraged due to browser differences and inconsistencies.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/Date

Couple solutions:

• use a numerical timestamp in the Date constructor
• use one of the parse functions in date-fns to safely parse your string. parseISO should work well here. https://date-fns.org/docs/parseISO

Good luck!