So it looks like my eero WiFi/gateway cannot handle the multicast ICMPv6 packets that #k3s is sending out (I still don’t know why it does this, but they’re legit packets). As soon as I firewall off the k3s box, the eero is perfectly stable again. Disable the firewall and the eero can’t keep TCP connections open for more than about a minute. Which is remarkably difficult to work with.

Hopefully eero will fix its issue, but in the meantime I’m back to reliable internet again.