Just to clarify: we are using a different method of writing text into Pro PDFs that retains many of the advanced parameters such as intercharacter spacing in text placement. So we can't just switch back to the way that ArcMap did it without bringing back some existing issues in text placement in ArcMap exports. We are evaluating a way to resolve this that does not lose those properties, and we'll put it in when we have a solid fix.
As a workaround, we found that it is possible to select ALL the text in the string and then retype the new string. I know it's not ideal, but that should at least let you replace the strings or edit them as needed.