I have a user on 8.5.1 and whenever she attaches a file to a new email message, it takes around 10-15 seconds for the attachment to appear in the message after she clicks ‘open’ in the attach file dialog box. It happens every time, regardless of file type or size or location. No antivirus app is running on her PC at the moment. The issue has only occurred on her current PC, which is several weeks old.
Cheers…