I faced the same problem, namely the false notification ‘A duplicate of this post was made. Please note that any changes you make to this post will be replaced when the duplicated version is republished.’.
It seems to me that Yoast Duplicate Post Plugin doesn’t remove an entry from wp_meta table with the key _dp_has_rewrite_republish_copy after republish is done. As soon as I removed it manually from database, everything got back on track and Rewrite & Republish button appeared again.
@mikes41720 can you look at this, please?