The value of Steem against the dollar is currently in decline - and since your rewards to be claimed are on Steemit - such has a knock-on effect.
I am also of the impressin that the decline in Bitcoin currency rates has also had an impact here.
So, the short of it is: If you made $0.50 in votes and the rate of Steem drops 20% then you'll actually see it go down to $0.40.
I hope that I understood your question correctly.
thank you i got to know about this