As you add citations to your document, Zotero will often need to update the other citations in the document and the bibliography to reflect the new one. When working on a large document, this process can be time-consuming and slow down your writing. To speed up the process, you can disable automatic citations update. This option can be accessed in your word processor (Word or LibreOffice) by clicking on the Add/Edit Citation button.
The citations will be displayed with a dashed underline. 
When you are ready to submit your document, remember to click the Refresh button on the Zotero toolbar to update the citations.