The first two bytes of the internal form ID refer to a non existing index of the Master Files list on the File Header record for the plugin.
This means it can not be determined if the record is an overwrite (and which master plugin it belongs to) or if the record is added as a master record by the plugin itself.
This can happen when entries are forcible removed from the Master Files list for example.
In case the plugin is a the result of using a merge tool, it might be possible to fix it by loading and saving the plugin in Creation Kit or xEdit.
In most other cases the plugin is most likely broken beyond automatic repair.
