For the sake of those who may come after, here is the reply from the module author:

The error you get occurs when PDF::Reuse tries to transform a page to an "XObject". There are many content streams forming the page and the program doesn't continue. Most often the procedure to concatenate streams really works. I think it has only happened to me once, that it didn't. Then Acrobat refused to change anything with the text. The font was strange and Acrobat couldn't do anything with it. Your case might be one of these cases.

Anyway, you could perhaps try to use prSinglePage instead. It accepts many content streams for one page, but you have to change your code a little. Look at the documentation. prSinglePage creates a new content stream of all your new text, and adds it to the array of streams. It puts it at the end of the array. So if it is possible, try prSinglePage.

jdtoronto