Visibility Plugin fails to update

ServiceRocket's Visibility Plugin fails to update in Confluence 5.5. We tried updating from version 2.1.1 to 2.1.4 so the plugin would be compatible with our version of Confluence. However, the plugin fails to update and we eventually need to restart the server. We tried updating it via the Marketplace link, downloading and uploading the plugin, and finally, disabling it, removing the plugin and uploading the plugin. Nothing worked. This plugin is important to our upgrade.