If your hashrate is unstable, or there exist large gaps between your local and online hashrate, inspect the following conditions:
1 Wait for a longer period and check your average online hashrate after a consecutive 24-hour-performance.
2 Unduly overclocking could be the primary reason in most cases.
3 Find your problem in the software logs.
4 Do not use any software that steals your hashrate. Be sure to set up a standby mining pool with a different sever. There won't be more than 5% difference in hashrate if your rigs run stably.