As an edge case, if you install another instance of an already installed plugin and that plugin installation fails, the cleanup from the failure will also delete the dataset for the first installation of that plugin. As a workaround until this is fixed in 11.3, it is recommended that users wanting to install another version of an installed plugin perform the installation from the CLI, using the -k switch:
iocage fetch -P -n PLUGIN_NAME -k RESTOFPARAMS