This must have been caused by a recent update - thank you for letting us know. We are working on a fix and will get back to you shortly.
Every time I go to edit an Ad Placement neither of the radios for "Only" or "All Except" are selected, even though I had set them previously. So, if I don't remember to select the radio again, even if i'm just updating the name or description it loses all ads on those pages because it submits the form with neither radio selected.
This is a relatively simple coding fix to pull in the value and set the radio to selected if the values match. Can someone work on this fix because this is a major annoyance!