With all my RX580 8GB on Win10:

PhoenixMiner.exe -rvram -1-rxboost 1 -clKernel 3 -eres 1 -> No hashrate
PhoenixMiner.exe -rvram -1-rxboost 1 -clKernel 3 -eres 0 -> 32.6 MH/s
PhoenixMiner.exe -rvram -1-rxboost 1 -clKernel 1 -eres 5 -> 32.3 MH/s


If -clKernel 3 can't use on next DAG epoch?