I just wanted to check back in and let you all know that I checked in with our support staff and there are no open bugs being investigated right now. The only issue was a reporting issue that was resolved last week (the one I mentioned when I first posted).
The most common scenario we're seeing in relation to a drop in impressions is the result of advertisers hitting their budgets sooner than expected due to the increased volume now that the search alliance transition is complete. If you haven't hit your budgets and your ads are not serving, please contact our support staff so they can investigate: [community.microsoftadvertising.com...]
adCenter Community Manager