I am experiencing an issue with my EAP670 where IPv6 UDP traffic is being dropped when using 3 SSIDs with their own VLANs. I have tested both the latest stable firmware version and the beta firmware provided at the following link: https://community.tp-link.com/en/business/forum/topic/577390. I have used iperf3 to test UDP traffic and have found that IPv4 traffic has no issues. In an attempt to narrow down the problem to the EAP670, I tried using a Unifi AP with one SSID enabled and the UDP traffic worked as expected on that AP.

I was able to reproduce this issue by resetting the AP, adding 3 SSIDs, and then enabling the VLAN on one of the SSIDs. The SSID with the VLAN enabled does not seem to pass UDP IPv6 packets.

Here is a tcpdump from the router to to the AP:

vyos@vyos:~$ sudo tcpdump -nni eth1.20 udp port 5201
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on eth1.20, link-type EN10MB (Ethernet), snapshot length 262144 bytes
00:19:11.113500 IP6 2600:4040:5d7c:3102:3542:5f52:8356:dca5.60836 > 2603:c020:4000:9301:f777:df11:fc2d:db85.5201: UDP, length 4
00:19:11.130896 IP6 2603:c020:4000:9301:f777:df11:fc2d:db85.5201 > 2600:4040:5d7c:3102:3542:5f52:8356:dca5.60836: UDP, length 4

Here is a tcpdump from the device to the AP:

kyle@laptop ~ > sudo tcpdump -nni en0 host 2603:c020:4000:9301:f777:df11:fc2d:db85 and udp
Password:
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on en0, link-type EN10MB (Ethernet), snapshot length 524288 bytes
19:19:11.099589 IP6 2600:4040:5d7c:3102:3542:5f52:8356:dca5.60836 > 2603:c020:4000:9301:f777:df11:fc2d:db85.5201: UDP, length 4

It looks like the traffic from the WAN to the device is getting dropped by the AP.