I've noticed when the pool luck is low the website appears to report my hashrate as low too (after a run of bad luck - like now)
When I check my Ant it disagrees

Right now website says 165GH/s for my Ant worker
The Ant says 185 GH/s

Just wondering why

I've noticed it a few times over the last week, always when pool luck is extended bad run

EDIT : Then perfect timing pool mines a block