InDesign GREP help

This is kinda working for me

Find
(?s)((.+?\b)\K){16}

Change to:

~P

Reason why I say 'kinda' is when I run the search for Change All - it's taking 1 line and making 9 words.

When I just run by Change/Find (individually) it works fine.

Weird - I don't know why!

I'm sure there's a GREP expert with a far superior method than this, but I am curious as why Change All results in 1 page being 9 words. But Change/Find (individually) works... very odd...