The word processor plug-ins apply the “Default” (LibreOffice) or “Normal”/“Standard” (Word) style to generated citations and the paragraph in which they are inserted. The bibliography is rendered in a different style — “Bibliography” (Word) or “Reference1” (LibreOffice). As a result, inserting a citation with Zotero can remove formatting (such as indents, line-spacing, font size, etc.) from an entire paragraph and the citation can appear in an unwanted font or format. You can correct the formatting by adjusting the “Default/Normal/Standard” style (for citations) and the “Bibliography/Reference1” style (for the bibliography) in your word processor.

Place your cursor in a Zotero citation or bibliography. Then, choose the drop-bown button in the bottom-right corner of the Quick Style picker on the “Home” tab and choose “Modify Style”. Make the necessary changes to the font and paragraph formatting for the “Normal” or “Bibliography” styles and click “OK”. You can also change the formatting for individual citations using the options in the “Font” and “Paragraph” groups of the “Home” tab. See here for a guide with screenshots.

Place your cursor in a Zotero citation or bibliography. Then, click the Styles Pane button at the end of the “Home” tab. Click the Current Style title at the top of the pane and choose “Modify Style”. Make the necessary changes to the font and paragraph formatting for the “Normal” or “Bibliography” styles and click “OK”. You can also change the formatting for individual citations using the options in the “Font” and “Paragraph” options in the “Format” menu. See here for a guide with screenshots.

In LibreOffice, open the styles manager in “Format” → “Styles and Formatting” or by hitting F11. Right click on “Default” or “Bibliography”, select “Modify”, and make the desired changes to this style.