Yes, this is vitally important and I forgot to mention it (it was nearly 4am my time when I wrote this and I had just got things working again and thought I’d look in here to see if anybody else had the same problem). This is only a temporary fix to get things working again. Thanks for the reminder @david.
That fix didn’t work for me when I updated everything at 00:00 UTC this morning (ten and a half hours ago). I only updated my instance then because I saw signature verification had been fixed. Then I had to do the temporary fix described above. Is it feasible that my usual update didn’t pick up the latest code for some reason?