What reason for bit lower hashrate all the sudden ?

[miner2k18]

I have been mining a ETH based altcoin for a couple weeks now and have been getting 29.1 - 29.4 Mh/s pretty much stead for these couple weeks on a certain RX 570 of mine, but a couple days ago it went down to a steady 28.3 - 28.7  and has been staying there but absolutely nothing has changed that would lead me to a reason why. Is it possible a pool can change something about it that would get lower hashrate all the sudden ? 

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[RustySausage]

I had the same problem with an RX 470, cleaned the dust out and it started hashing like old times 

[ivakar]

Maybe it is overheating? I mean the spring is there, outside temperatures  are rising and your home temperature is higher as well and that might cause the hash rate drops  and are you sure you windows have not auto updated the drivers?