RX 470 drops clock a little and never returns while mining

[bughtoo]

I was selling my hashing power for a few days now and i have encountered a little problem that is pissing me off  

On my 2x 8gb rx470 Nitro+ i have been able to mod bios, OC them and get about 29mh/s (on ETH) out of each card (more like 28.5).

 

But when renting the has speed for longer(eg 4 hours, on nicehash(i know not the best way to earn with GPU)) the clock speed of both cards

drops to around 100/130 mhz less than max clock speed and stays there, that results in about 1.2/1.5 Mh/s less hashing power on each card.

To bring them back i have to manually in wattman increase/decrease any setting and press apply and it goes back.

 

No the cards are not thermal throttling, they are sitting at cosy 75*C. No i havent OCed them to hell, only 1280 on the core clock and 2100 on memory.

No i havent undervolted them too much 1020/1030mV at max clock speed.

 

Any ideas what might be causing this issue?