That looks normal

Which hash rate are you talking about, the numbers reported by the pool or the MHSav number under the Status -> Cgminer Status tab in the interface?

I sometimes see the pool reporting lower numbers than the web interface



which is something I can't explain (power consumption is also the same)

My current solution is to hard reboot the machine when I spot this

Can you make a screenshot of the Status -> Cgminer Status page?