CL-35B1 slow LAN speed

    CL-35B1 slow LAN speed

    Lan speedtest says that writing is 30Mbps and reading 120Mbps.
    My home network is all Gb compatible. I can have better results only for few hours after unplug/plug nas from electrical outlet. Then speeds are 160/360Mbps, an then speeds drop.
    Is there any way to have better network speed?