The plugin works just fine, even with the latest version of WordPress v4.9.2 as stated on the plugin page. You are trying to do this for blog posts, correct? Excerpts in WordPress only work for posts, not pages. Here’s proof that it works with the latest release:
https://www.renegadelife.org/category/news/
There are some themes that allow some overriding control over excerpts. For example, the theme on the above website (extension of the Sydney theme) has options in theme customization that forces the entire post to be shown. If these options are turned on, it overrides all excerpt rules including the Read More Excerpt Link plugin. While uncommon, check your theme’s customization to see if there’s any settings having to do with content length or excerpts.
Sadly, there are some themes that build their own excerpt function rather than correctly extend the built-in excerpt function. Basically, there’s a hook in WordPress that can be used to correctly extend the excerpt functionality, and that’s how Read More Excerpt Link works. However, if your theme doesn’t adhere to this WordPress standard, there’s no way Read More Excerpt Link can work as the theme has bypassed the standard method and used a custom and improper implementation. This would tell you that your theme is a little half-baked and the designer didn’t know what they were doing.
Hope this helps! Let me know if you have any questions.
