The bug that came with iOS 11.1 and simply did not allow some users to type "i" by replacing it with "A" and a Unicode symbol has just been fixed by iOS 11.1.1. This update also takes care of an issue with Siri ("Hey Siri" sometimes not working).
https://www.notebookcheck.net/Apple-fixes-the-autocorrect-bug-on-iPhones-and-iPads.262882.0.html