I have the same problem with my Primo. I asked Volumio Support and the answer is: “Please contact their developers. This is a 3rd party plugins, we cannot support and we don’t know how the plugin works and how it is written”.
When Volumio has an error uninstalling a plugin, it is in bad state that requires logging in with ssh and deleting and editing some plugin configuration files. For most people it would be easier to start over and flash a new Volumio image.