You are not alone with this problem for this particular block.  If you want you may raise a ticket on the Slush support page (see 'knowledge base' link on the left side of the Account Page, you'll need to register for this and then you'll be able to raise a new ticket).
Looks like there was some problem on Slush's side, which caused the reward of many people to drop to about 20-25% for this block.