Sorry, but I tried all three “read more” plugins including yours and all gave me significant problems. This was a new WordPress install.
Yours in particular would work on new posts, then not work on some imported posts but work on other imported posts. It didn’t work on the mobile version, and hiding it on the post page caused it to stop working entirely.
It was far too many issues for a brand new blog to deal with and I disabled and deleted your plugin. Best of luck with your endeavors in the future, but this plugin had too many bugs to be of value to me. I have enough work to do in several different endeavors without bug hunting on a plugin that I just don’t need.