Hi, i need help

After months of mining ETC with Claymore (claymore-eth-v10.0 - Simplemining), I noticed that the speed for each AMD RX470 fell down from 25.7 MH/s to 21.8 MH/s. then update at claymore-eth-v11.8

I tried other versions Claymore in Simplemining or restarting the machine but it always mines with lower speed.

Configuration:
7 GPU RX470
MoBo: Asrock H110 Pro Btc
Simple Miner
OS: Simplemining
OC: Core 1130/MEM 1830
powerstage: 1

Total: 180 MH/s @ claymore-eth-v10.0 - Simplemining