Best guess is that you were borderline awarding .01. However the $ calculations that show are a 3 or 4 day rolling average of Steem value. So, since Steem was falling you saw your vote $ amount decrease. It’s having a great day today, so as the average trends up, your reward should as well.
Second, your vote $ amount is dependent on how many other people are using their voting power. Imagine no one voted for a week. The first person to break the pause would see their single vote, regardless of how much SP they have, give out the entire rewards pool! As others voted after, the payouts would spread evenly again.
I only bring this up because the Steemit corporate account has been sitting on a lot of SP that they do not vote with, thereby giving everyone else a stronger vote than they normally would have. Recently Steemit has begun delegating big chunks (a couple million Steem) to deserving projects. With this SP being actively used now, you could be perceiving it’s effects on vote strength as well.