OK, so I figured a work-around. I guess YMMV. This is what I did:
PS: I have 7 email accounts set up, and noticed the signature field for the 7th account was missing entirely. I have the signature inherited from whenever I had set it last (from my iPhone 4 a couple years ago), and shows up in my email, but the field to edit it is no longer visible.
Hopefully this trick helps someone here.