I wondered because you specifically mentioned attachments. Some attachments are displayed below the message body in the preview and might be mistaken as being part of the message body or even all of the message body, but they are never within the message body as you have said. Attachments are separate, hence the name.
In your print preview screenshot, Appointment.ics is an attachment. It will not be printed.
Can you give screenshots showing the difference between the message in the preview pane (that is the regular place for reading your messages) and that in the print preview popup.
I suspect as @Gary says eM Client is reading the .ics attachment which normally shows it in the body of the email ok (when viewing the email), but doesn’t normally show the .ics attachment in the print preview as its an attachment and not pasted inline into the body of the email as well.
This sort if thing also sometimes happens when i get .jpg ,.png files that are just attached and not pasted inline as well. So nothing shows in the print preview window, but does show ok when viewing the email.
Google .ics attachment invites for whatever reason appear automatically in the body of the email and the print preview window, so i suspect they automatically generate both when sending the invite .ics.
What i do with the attachments that won’t print preview is “Screenshot / Screengrab” them and paste them into a paint program like eg: Paint.net for Windows or Paintbrush for Mac and then Print them from there.
You changed the subject to Solved. Though it is not actually a solution, did you solve it by the screenshot workaround that @cyberzork gave? (I was not sure from your reply)