Can't edit post anymore!

I can no longer (find a button to) edit the post I’ve been re-editing every so often for many months now: Sci-Fi book for each month

This breakage seems really random. There’s no indication that the topic is closed or locked or anything.

Can this be fixed?

I’ve looked at this and am able to edit it. I don’t see settings that set a time frame for no longer being editable. Were you logged in when you tried?

Yes, I’m logged in when I try this.
The closest I get to editing is to click on a “8 // Sep '14” thing, where the // is a pencil icon, and it shows me the edit history (containing about 8 edits).
Guess I should get a wiki account instead.