1. Make sure netCut running on PC connect to same SSID as the controled speed’s/ the device. some router has 2.4 and 5G two SSID name. take a look .
2. make sure don’t use mesh WIFI.
3. make sure disable IPv6
4. check the router security setting , if there are anti ARP setting, make sure it is Unchecked. it could has name as “MAC binding” , “ARP binding”. VLAN etc. make sure disable those.