What word processor and version? What operating system? You can upload your screen shot to any cloud storage service that allows public access, (Dropbox, Google Drive, etc.) and paste a link here.

I've had this happen with an older version of LibreOffice when pasting text with 'decorated' characters or some ligature combination-characters. In my case, when this happened, I wasn't using Zotero. I think that this had to do with an unorthodox character encoding from the source document and LO not knowing how to compensate for the peculiarities.

edit - I haven't encountered this problem with newer versions of LO nor with Zotero.

@Olib170 You should make sure that you modify the font size in the default document style instead of manually in the paragraph. Zotero inserts text that has accents differently than one without it due to technical reasons and the former is more likely to have issues restoring an in-line style.