I've also had the same problem as of today. I had one ad group that has been running for a while, with .30p (UK) bids, but now the minimum bid has risen significantly to £2.50, and the QS for the keyword has changed to poor. Before it was at OK. The keyword is very relevant. It's a keyword that has become popular to mean something slightly different than it originally meant, and Google can't see that it's highly relevant in terms of the landing page and website it is used in (in it's new meaning).