Don't know if this helps anyone else, but I was able to resolve this by starting gparted and exiting. Based on some other bug reports, gparted prevents automounts while it is running: https://bugs.launchpad.net/ubuntu/+source/gparted/+bug/134712
Although the exact case in the old bug didn't apply to me, I just ran gparted and closed it and now things are automounting.
Don't know if this helps anyone else, but I was able to resolve this by starting gparted and exiting. Based on some other bug reports, gparted prevents automounts while it is running: https:/ /bugs.launchpad .net/ubuntu/ +source/ gparted/ +bug/134712
Although the exact case in the old bug didn't apply to me, I just ran gparted and closed it and now things are automounting.