I see that many people here don't understand the miners table on Zpool and HashRefinery.
Under the miners table you see a "live" hashrate calculation based on your recent shares. That number WILL FLUCTUATE! It's normal.
You'll see a wild fluctuation depending on algorithm, ranging from 20% to 60%.
I'm constantly mining on these pools using profit switching with my in-house developed software. Nist5 and Neoscrypt are frequent algos we mine and I don't see any problem on the poolside.
Our scrypt miners report 200-800MH/s but they always average 550MH/s (slight overclocked, matches hashrate on miner side)
So it is normal, check the hashrate graph, not the live report, and if you mine for short periods It's like flipping a coin.