I have a Macbook and an Android device (Oneplus phone) on same network and the Macbook connects via USB LAN (or Wi-Fi), Android device via Wi-Fi. I detected the following anomaly:

• I can ping the Oneplus from the Mac:

64 bytes from 192.168.1.127: icmp_seq=3 ttl=64 time=30.433 ms
--- 192.168.1.127 ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss

• I can ping the router from the Oneplus
• However I cannot ping the IPv4 address of the Mac
• I took a look at the traffic in Wireshark and I got the “host unreachable” message to the ICMP requests
• I also started to host a simple HTTP server, but it seems the Mac does not response to the TCP SYN segments, because I could see RTO flagged segments (Retransmission Timeout). (3-Way handshake never completed)
• Fan fact, recently my ISP started issuing IPv6 addresses and I tried to ping the Mac from the Oneplus:

--- 2001:*:*:*:*:*:*:7e50 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 6.737/33.397/108.664/43.467 ms

It was working as the above log shows.

Mac's firewall is disabled and there is no firewall rule applied in the router. I removed all network interface under the System Preferences / Network menu and added them again.

I also selected the Link-local only option at the System Preferences / Network / interface / Advanced / TCP/IP / IPv6 Configuration tab. Unfortunately none of them worked.

My question is why did IPv6 ping work and IPv4 not? Could be the problem the recently introduced IPv6 addresses?

[Edit]

I created a Hotspot with my iPhone and connected with both of the Mac and the Oneplus. This Hotspot does not have any IPv6 configuration, but I experienced the same issue.

I also created a Hotspot with my Mac to eliminate the router from the circle and I connected to it with the Oneplus. Like every time, I could not ping the Mac, despite the Oneplus gets IP address via DHCP from the Mac. (So there was network traffic)