Invisible character "" (U+FFFC) inserted at end of dictation input on iOS.

A user reports:

Reporting an odd bug that I have not been able to get around. When using dictation on iOS, a bizarre character is added 1 to many times and is not visible on mobile - but when reading the message on desktop app or web - it is visible. From the various tests I've done I was able to partially correlate this to the blue squiggly auto-corrections that iOS is recommending after dictation is finished.

Here is the character that appears after using dictation: sample message 

Anyone have any insight into this OBJ character and what causes it, can it be avoided, etc?

It renders the dictation function unusable because when you dictate a multi sentence response, it is peppered with these characters.

Looking around our issue tracker, it looks like we've had at least one known bug with dictation on iOS before this: #2659. The problem there was in some code in React Native, and it was solved by taking a fix in a new React Native release.

There's another bug in the React Native tracker that looks different from that one, and seems like a plausible explanation for the current bug, but I haven't dug deeply yet: facebook/react-native#22139. Unfortunately, that one was unceremoniously closed and discussion was locked by a maintainer after that maintainer confirmed that it was a real bug.

I think a good first debugging step would be to check and see if onKeyPress is being called in our case, at the end of a dictation input. And if so, with what character.