Please enter a valid URL (e.g., yourwebsite.com) error on valid urls

I'm having an issue with the read more builder that has been happening for a while. I've contacted support but ended up nowhere. When I try to hover over, edit the read more button and put in a URL it says enter a valid URL. Here is an example of the URL: https://lasentinel.net/dodgers-fall-to-white-sox-on-black-heritage-night.html I tried shortening it using a service. It seems it will not accept any URLs from this site. Is something missing in the HTML that it's looking for? What could be causing this? Thanks