https://www.theguardian.com/technology/2017/nov/06/bug-stops-some-iphone-users-typing-i-replaced-with-gobbledygook

Glitch in predictive text system making messages illegible for some iPhone, iPad and Mac users, while Apple Watch bug crashes when asking for the weather

A bizarre predictive text error has left some iPhone users unable to type the word “I”. Instead, every time they attempt to use the English first-person pronoun, it gets replaced by the letter A and an unprintable unicode character, typically rendered as a question mark in a box, but occasionally five horizontal bars instead.