I cannot seem to edit an e-mail in my Drafts folder. Initially, I received a msg stating, "cannot load editor." A second attempt just seem to hang. I like many of the features of the new e-mail version, but it does seem noticably slower and a little buggy.
I cannot duplicate this issue. Try clearing out your browser's cache/browsing history. When you have done that, close out the browser and re-start it in a fresh session. If that doesn't do it, then try using a different browser.
The specific problem I experienced seems to have gone away. It may have been related to some Windows 10 updates that were taking place when I attempted to edit my draft e-mail.