I have the same problem! I did not find solution to the problem! The card is very bad! I have sapphire nitro R9 380x.
1) Check your Power Limit (must be set to +50/+20 (depend on max value you have))
2) Check your ULPS Status. Disabling it can help with some voltage drop problems (lags, FPS drops and such). If your card from Sapphire, you can use Sapphire TRIXX to disable ULPS.
3) Check your PSU Voltages - how old are your PSU? Use HWMonitor to check system voltages in idle and full load mode. Also check temps - very high values can make your hardware unstable.
That's all for now. Hope it helps