I have users experiencing the same thing, MYOB AR SE latest version running office 2016 LTSC, i got in touch with a tech yesterday and was told 2 conflicting stories one being that SE no longer supports signatures (which they backtracked on once i tried to reconfirm) and the other blaming an update within outlook.
However if the update to outlook was the issue then our users runnung MYOB AR on their desktops and the same version of outlook it would also not work there however it does. so i also agree something within Server Edition is to blame for this.