Yes, mining is like gambling Sometimes you are lucky and find a lot of shares and your effective hash rate goes way up, but sometimes you have unlucky streak and your effective hash rate will go very low. In the end it should average to your actual hash rate or very close to it over time.
Here is my current chart.
https://image.ibb.co/kyyLLk/hash_chart_eth_09may17.pngSame here.
I doubt it's an unlucky streak, since I know several people that are experiencing the same thing since a couple of days.
The number of shares just dropped by about 20% a couple of days ago on ethermine.org pool.
What could be the reason?
I'm also on ethermine and my last 24 hours looks like yours. The higher your hash rate the more noticeable the drop. My effective hash rate went from just under 1GH/s to 942MH/s. If you look at the stats for the top 10 miners on ethermine, you'll see that almost all of their charts show similar drops.
