Think you might have loaded a resource more than once? Let Zotero help you find it and merge the records.
In Zotero Desktop you will see the "Duplicate Items" option under "My Library" and before "Group Libraries"
When you click on this you will be shown your records that could be duplicates and be able to merge them
Sometimes when you add a resource not all the citation information is correctly listed and/or the parent item hasn't been created. In Zotero a parent item is where the citation lives, the PDFs and links are attachments. Without a parent item you won't get proper citations in your work.
Anytime information is incorrect in a Parent Item you can edit it by going into "Info," placing your cursor in the appropriate field, and typing in the correct information. Be sure to select an "Item Type" that best matches what type of resource the item is and be sure to use the plus symbol to add more authors.