Power's instability will cause this problem. The more stable of the power supply, the more stable of the mining. A better USB 2.0 hub helps lots here.
NOTE: some hubs have a surge protector. The surge protector will limit the current that drew by mining device. It will kick off the device when there is a surge. These kind of hub is NOT good for mining. A self powered hub with surplus power is the best.

We will keep fine tuning our software to improve the stability. A planing software feature is periodically check device status. If find a device stop mining, the software will try to stop/restart mining thread. Hope this method will improve stability lot.