I'm setting up a new homelab dev server, and am seeing IPv6 connectivity problems, but no issue with IPv4.

Working through the prerelease of #n4sa2e by @mwl to troubleshoot, but I thought I'd also ask here...

Any troubleshooting tools I should try next? Both computers are on the same LAN, with 3 switches (Unifi and Cisco) in between them (they are in different rooms). No VLAN or router between them.

My initial hypothesis is that ndp is not working well on one of the switches and IPv6 packets don't know where to go "sometimes"...

Initial test between desktop and devserver (both running FreeBSD 14.3) - run ping for about 15 minutes (manually started and stopped in two terminal windows within a few seconds of each other)

desktop$ ping -6 devserver
--- devserver ping statistics ---
903 packets transmitted, 249 packets received, 72.4% packet loss
round-trip min/avg/max/stddev = 0.092/235.931/2913.590/598.160 ms

desktop $ ping -4 devserver
--- devserver ping statistics ---
899 packets transmitted, 895 packets received, 0.4% packet loss
round-trip min/avg/max/stddev = 0.096/0.241/0.529/0.035 ms

My next tests will be to have them both connected to the same switch, and see what is visible in the arp/ndp tables.