What the hell is happening with Akismet spam filter?

From two days I got more than 50 spam comments in my blog that is not automatically marked as spam by Akismet. But when I check the comments and click ‘Check for spam’ it is then identifying them as spam. I don’t know why it don’t work automatically as it was doing earlier.

I tried reinstalling but with no luck. Anyone has any idea regarding this or faced same issue?