That makes for some nasty debugging and unsafety. Both sides should parse both times, unless you're encountering real (not imaginary) performance issues.

As someone who's been parsing everything entering the system from 2018, I don't believe you can have performance issues by parsing the data entering the system, the only exception I can name in a decade was real time trading app where the data coming in all time was just gargantuan that parsing it all the time was impacting UX and even then there should be an argument for the backend insisting on sending whole data instead of the latest value.