So I duplicated the #scrivener project on my iPhone. Once it synced to my Mac, I opened it. Everything is perfect. I can't tell you how many times this has been the fix for weirdnesses in the software's behavior... because I haven't counted. Half a dozen times, at least? Anyway, I'll just rename the projects and delete the problematic one. Just to be real, I could have restored the damaged project from backup, but I didn't want to risk loosing current work.