serious mail sync problem between ipad and macbook

Hello

on my Ipad / Mail ( IMAP account ) I recently opened a draft that was left opened on my Macbook Pro ( High Sierra 10.13.3).

Although the draft was saved again on my Ipad, it could not be opened neither on Mac nor Ipad. Both drafts were blank, the programm unable to load.

Any suggestion to recover a rather important mail ?

Best