Concerning the drop in @mentions. We retrieve all your @mentions from different API endpoints including search. These sometimes contain non-native retweets (e.g. "Cool! RT @square etc..."). These should count towards your retweets and not your @mentions and so they are removed at a later stage, which would account for the drop you've been seeing.
In general we get your @mentions once every hour from the Twitter API and a couple of times a day via search.