According to MacRumors, not everyone is affected by the issue, but it is possibly linked to the emoji keyboard, where a strange letter I symbol is in the frequently used for most people that are affected by it.
THE FIX: Apple Customer Support is recommending using replacement text as a temporary fix for this issue, however they are currently working on an iOS update to permanently fix the problem. To do this, go to Settings > General > Keyboard > Text Replacement. Type in an uppercase “I” for the phrase, and a lowercase “i” as the replacement.
We hope that this has helped you, and encourage you to share this with anyone you know that may be experiencing the same problem.