One person received a response from Yahoo, where Yahoo presumingly said:
Upon researching your account we found there is a known issue causing frustration among many clients. Our reporting systems went down at approximately 8pm on Monday evening. However we have created a case for you within your account and are currently working to get this resolved as soon as possible. Please be patient while we work to resolve your concerns.
So since Monday night, some advertisers are still without accurate reporting data for their search ad campaigns.
I am not sure if this is related to Yahoo testing Bing powered ads or not, but it is around the same time.