Sometimes, if a user has a draft that is more than 30 days old, the draft deletion task will delete the chapter(s) but leave the Work object behind.
Not only does this leave the draft blurb visible on the user's drafts page, causing confusion (the user gets a 500 error when attempting to open or edit the draft), but if the work was in a collection, it can also cause 500 errors for moderators attempting to reveal or de-anon works (or, I believe, access the Manage Items page).
It's possible this is also related to tags used solely on drafts still showing up in the wrangling bins even when they are more than a month old.
Unfortunately, this is not something we can reproduce on demand, but it appears to be happening with increasing frequency.
We will add more details when/if we get them.