I finally got yesterday's post up by generating the HTML from my Org source file and then pasting it into the WordPress editor. I'm still not sure what's happening. Very occasionally I can push a post with
org2blog but most times it gets an error and hangs Emacs.
org2bog and updated all the packages. Now I'm about to try to push this file. If I have to paste in the HTML again, I'll add an update. In the meantime, if anyone else is seeing this problem, please leave a comment.
UPDATE 2016-09-21 14:06:08: OK, that worked but I'm suspicious that it might have been one of the rare exceptions. If this update pushes too, I'll be more confident that things are back to normal.