Thank you, yes this happens with the latest drivers, with Compute mode selected. 

Thank you for the link, will check it out.

I've an issue I was unable to solve after spending days searching and investigating.

I’ve modded few cards MSI / Gigabyte, 570/580.

Very basic mod - timings shifting, and undervolting to 950mV.

All of them of them exhibit the same pattern – start mining high speed 27 - 28MH, and then – few minutes to few hours – drop performance to about 18-20MH.

Tried MSI 570 and 580, Gigabit 570 – all have the same pattern.

Different cards with Samsung or Hynix, different motherboards, different risers, quality power supply (EVGA 1300, tried different models), single or multiple cards.  different driver versions. Same behavior.

Use claymore in eth - only mining through nicehash.

Thanks a lot for any hints!