Same thing happened to me. Thankfully I noticed it today when I was checking tonights recordings, or I would have missed recording Mad Men! Not only did all my AMC scheduled recordings disappear, but AMC 731 disappeared from my Favorites as well. I had to add it back in, and re-enter my series recordings for all AMC shows. Very weird.
Same thing here. AMC disappeared from my Favorites list on all my DVRs and STBs and the scheduled series recordings - including future episdoes of Breaking Bad and Hell on Wheels - were listed as being set for channel "0." Had to re-add it to my Favorites and also set up the series recordings again.