I have used your plug-in before and it worked perfectly.
I installed it to my newest client's site (local only) and have hit a critical error. I tested out the plug-in on one post only - in this case the post titles was "2020". Went to the Bulk Title portion of the plug-in. entered my SEO title, saved and viewed the page only to get a 404 error.
No problem, I thought. Did some investigating, resaved permalinks, etc, but still no fix. So deactivated the plugin and I was STILL getting a 404 error..What?
Went to the post directly. It was still there. URL was correct. Everything checked out.
In the end I was never able to get that one post to work again. I even deleted the post and re built it. I STILL had a 404 error. WTF??? Deleted the plugin and still no success.
So I concluded that post must have been corrupted in the database because I can not make a totally new post with title 2020 as it gets a 404 error.
What do you think?