Strange symbol in the place of capital I

It was a bug that Apple has fixed. iOS 11.1.1 was released today and it fixes the bug. Update your phone.

You have not told us which app this was in

Presuming it was in iMessage - I would start by force restarting the phone

For any iPhone 7+ and below -

After shutting down all open apps using the app switcher - invoked by quick double press of the home button and swiping up on each app till it flies off the screen.

Hold the sleep/wake and home buttons down together till you see  logo - then release and allow normal boot up

For iPhone X -

To perform a hard reboot on the iPhone X, press and quickly release the Volume Up button, then do the same for the Volume Down button. Follow up by pressing the Side button, and hold until the display suddenly shuts off — about 10 seconds. Keep holding the Side button and release when the device turns back onto its Apple boot screen. This is the same process the iPhone 8 and 8 Plus use to force-restart, too.

(Adapted from here)

In most instances that should fix the issue - please let us know if it does not

There is an iOS update that is supposed to fix this.

If your still having this problem update you phone 😊

In case you didn’t notice, there was an update that fixed this.

My phone started dong that yesterday: 11/08/17

Same thing is happening on mine and then changes to A. with a power status bar next to it when you copy and paste the text .

This does not take care of this issue on all affected phones.