If you are on IOs 11.0.3 & 11.1 there is a bug that replaces the letter "I" with "A[?] in your text messages. This weird activity appears as the primary entry in your IOs predictive auto-correct text feature. Your letter "I" is getting replaced with "A[?]" If you don't notice this error you are sending malformed messages.
Lots and lots of users in the Apple community have spotted and reported the error last week and this past weekend on twitter and on forums.
Apple has acknowledged the bug and is telling users to set up a text replacement rule:
- Go to Settings > General > Keyboard > Text Replacement
- Tap +
- For Phrase, type an upper-case "I". For Shortcut, type a lower-case "i"
Users who have listened to Apple say this this technique works. As another suggestion I recommend to disable your predictive text auto-correct feature. Disabling the feature will not make it go away, but the bug will not take place in your situation. You can also install custom key board apps. The bug should be fixed in the next IOs updated.