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Well you don't see real quality scores for the Content Network.
The advertiser(s) could have blocked you, or gone to a different ad format. Someone could be outbidding you.
Did you visit the sites and placements where your ads used to run, to see what's there now?
I haven't seen any major changes across my accounts, some of which are only Content.
I sure would not bet on the Quality Score you see in the AdWords Editor being all that accurate for the Content Network.
Quality Score is figured differently for Content; it's not so much based on a single keyword but rather a theme.
Were these changes you speak of last Saturday published somewhere or are you just refering to changes you noticed in your account?
I know before one did not need to add keywords which I have not but maybe one does now?