regarding the hashrate drop on gridseeds
I do not have gridseeds, only 6 r9 270x cards and cgminer reports a constant 500-505 on all 6, this should come out to 3000-3030 hashrate, on wafflepool website my 15 minute hashrate shows 2.84-3.30MH/s, while my cgminer still shows 3.0MH/s
So i dont think it is a gridseed specific problem
What does you WU show. 3M Hashrate with a WU of 2.8M is 2.8M to the pool not 3M. The pool only counts the accepted work you submit.