If you use an exclamation mark (!) in the blog title field, the blog URL will include that exclamation mark even though the URL slug dialogue doesn't show it to be so.
After careful checking, I confirm that:
The URL without the exclamation mark will throw a 404 error (page not found)The URL with the exclamation mark loads OK
The XML Sitemap (used by search engines to find all your pages) incorrectly shows the URL without the exclamation mark. This means it's likely your post won't be indexed, and so less likely to appear in Google search results. As a result, any post where you've innocently used an exclamation mark in the Title tag will not contribute to your site's SEO performance. I didn't check if the same applies to Pages, but its reasonable to assume this might be the caseCheck it out and let me know ;)
I checked if my Client's post was indexed using a site: <URL> in a Google search, and this revealed the page wasn't indexed. I also confirmed the post wasn't indexed via Google Search Console.