FOUND THE PROBLEM: a too-full MySQL database from 1and1. Nothing to do with what I was doing at all.
Minor update:
I tried posting something as a test just now to see what would happen and I saw that the button was not the previous PUBLISH, but is now SUBMIT FOR REVIEW. I pressed it but received no notification or alert. No new accounts have appeared under “administrator” either.
I also tried logging in with a backup administrator account and got the same results.
