I just experienced the same problem for the second time, and can't figure out what's going on. I had "Allow Comments on all posts" checked in the back end, and had the "Allow Comments" box on each post checked. Out of the blue, they all unchecked themselves. I went to my site and noticed "Comments for this posts have expired" or something like that in the comment area of each post. And this applied to all the posts, not just a few.
So the only solution I could see is to go back and manually turn those back on in every post, and turn "Allow Comments on all posts."
The frustrating part is this is the second time this has happened recently. Anyone else experienced this? I tried searching. Not sure if it's a plug in issue or what. But it seems to be happening out of the blue, not immediately after something has been edited.
site is http://www.jaredsouney.com