iphone – What is this weird locale and how do you fix it?

One of my apps isn’t working because the iPhone is reporting a null locale. Even when setting the language and region to English/USA, this is the result on the Language & Region screen:

unknown currency sign

and the bug in my app still occurs. That’s 0xa4 “currency sign” at the bottom, according to Wikipedia:

The currency sign ยค is a character used to denote an unspecified currency.

So it seems that even iOS does not understand the locale. How does this happen with a real phone and how do you fix it?

This is an iPhone 12 mini on iOS 14.7.1. Unfortunately it’s not my phone so I have limited access to debug it. I have not been able to reproduce on my own devices.