When you type the letter "I", before hitting Space, tap the "I" that appears in the box.
An online discussion forum on Apple's website includes comments from victims of the bug.
These fixes aren't ideal but they'll do the trick until Apple issues an update to A [?] OS 11.1.
Go to Settings, then General, then Keyboard, then Text Replacement. The bug seems to affect iMessage and other apps including Twitter and Instagram as well. "When I tried to copy and paste the content of the tweet, my paste fixed it and just showed the letter 'I'".
Autocorrect suggesting a change for "I". Even if your phone can type the letter "i", you'll likely still see the garbled messaging if it's been sent from a device that has been affected.
Apple has patched a number of bugs in the past year, with many related to security, as TechRepublic's Brandon Vigliarolo reported. The switch has impacted users on iOS 10 and 11.
"Also included in the update is the Love-You Gesture, designed after the "I love you" hand sign in American Sign Language".