This is followup from last post about connectivity issue between two computers in same subnet, somehow the arp -s workaround stopped working. I have tried different ways to figure out the root cause, including using tool like tcpdump to sniffer ARP/ICMP request/response, but no luck.

I doubt it’s caused by the wifi router, which model is Zyxel nbg-418n. Eventually I found the workaround to add static DHCP table for one of the machine, and everything works magically.