Thank you for reaching out and sorry to hear you are unable to export assets. We would like to know the XD and OS version of your machine. Does that happen with this specific file? If yes, is it possible for you to share the XD file so that we can investigate the problem at our end? You can upload the file to a shared location such as CC or Dropbox and share the URL with me over a PM.
So that we can try from our end, try to resolve ASAP.