Ipv6 config issues

My Setup:
I'm using 2xWAN connections through mwan3 on openwrt 21. My router is Xiaomi 4a gigabit connection

One of my ISP started providing native ipv6 recently. For that interface I created DHCP v6 client. I added this interface in mwan3 as well. Now I can see all 3 interfaces online (wan, wanb & wanb_6) My laptop is also getting ipv6 address in LAN.
Everything seems to be working, except when I try to do ipv6 test (on https://test-ipv6.com/), I get this message

|Test with IPv4 DNS record||ok (0.432s) using ipv4|
| --- | --- | --- |
|Test with IPv6 DNS record||timeout (15.011s)|
|Test with Dual Stack DNS record||ok (0.807s) using ipv4|
|Test for Dual Stack DNS and large packet||ok (0.751s) using ipv4|
|Test IPv6 large packet||timeout (15.015s)|
|Test if your ISP's DNS server uses IPv6||ok (0.528s) using ipv4|
|Find IPv4 Service Provider||ok (0.596s) using ipv4 ASN 55352|
|Find IPv6 Service Provider||timeout (15.014s)|

Which signals to me ipv6 addresses aren't resolved correctly. If I go into network->diagnostics and do ipv6 ping test on openwrt.org, it is also failing with message:
PING openwrt.org (2a03:b0c0:3:d0::1af1:1): 56 data bytes

--- openwrt.org ping statistics ---
5 packets transmitted, 0 packets received, 100% packet loss

Can anyone tell me what I might be doing wrong?