the o365 office add-in’s cached add-in is null

 let timer = setInterval(getOfficeItem, 1000);
 function getOfficeItem {
     if (Office.context.mailbox.item) {
        // Your logic
        clearInterval(timer);
     }
  }

Above is a block of code that I was able to come up with to await the Office item on an ItemChanged event

Update: This seems to have been fixed for replies but not drafts.