It’s an issue with the old version (0.9.6) of the “com.gradle.plugin-publish” plugin prior to 0.9.7 that you are using.
There was a bug in versions prior to 0.9.7, where artifacts would silently not be pushed into the repo, which means the latest version of your plugin will not work properly when people apply it to their build.
Upgrading to the latest version (0.9.9) of the plugin-publish-plugin will fix this, but this will require pushing a new version of your plugin.