Monero hashrate drops when you disconnect your monitor (even if you are on IGP), or the screen power shut down after a while.
Simple disable screen power shut down, and do not disconnect your display while mining.
When i disconnect monitor , my hashrate still stable. But when i run gpu-z or hwinfo --> drop. I don't know why. I prefer mining without it, and hashrate seems to be stable around five days.
https://s1.postimg.org/59pinvrs6n/vega.jpgTry it.
