Today I did a fresh WordPress install on my localhost. And the first thing I did after installation was installing your plugin for testing purposes.
But even on a fresh install with no other plugins or themes or things like that standing in the way, the same issue occurs. So I am pretty sure it is a mistake in the plugin itself.
For me it is not a problem anymore because the issue I was dealing with that made me install the plugin in the first place Is not there anymore. I have solved it in an other way.
I wish you good luck in the further development of the plugin.