When you send an email that was cloned from a previous campaign and updated, the sent email shows the old content rather than the new content.
This can be caused by Dynamic Content in the email. If you clone an email with Dynamic Content but only update the default content, then the old content will be sent to leads who are not part of the default segmentation. Open the email in the editor and see what email elements are displayed in the Dynamic tab.
Check the different segments in the editor and see which ones have the old content. You can update the dynamic content for each segment or simply make the content static, which will make the email use the default content for all leads.