If you already did factory reset and didn't work try this method below.
I don't have much experienced about this miner but I heard someone experience that their hashrate drop after upgrade to the latest firmware. And they try to change something like "PLL" and the performance was increased but everytime they restart the miner the PLL that he setup is turned back to the default setup.
I don't know if it will but you can try it.
You can find the PLL on the dashboard under system configuration it looks like this.
Then get some idea from this post
https://bitcointalk.org/index.php?topic=2621350.msg35513443#msg35513443.
