Does anyone out there have IPv6 on WiFi (not mobile) working stably with their Pixel phone running GrapheneOS?

I have a Pixel 7 that has been running whatever the latest GrapheneOS release is for the last 6 months (Currently Build TQ3A.230605.012.2023062300)

During that time I've never been able to get IPv6 on my WiFi working properly. IPv6 on the mobile network is fine.

What happens is, when my device initially connects to the WiFi network it gets an IPv6 address and has IPv6 connectivity but then after a minute or two (it varies) it loses the public IPv6 address. There's no problem with IPv4.

All the other devices on the same WiFi network seem to be working fine (Windows 10/11, IPhone, IoT devices).

A few things I've tried to no avail

Changed the IPv6 Router Advertisement (RA) interval on the router to various short, medium and long values (e.g. 3 seconds, 15 seconds, 1 minute, 10 minutes)
Tried modifying the RA lifetime on the router (Values between 600 - 9000 seconds)
Under the Wifi settings for the network on the phone, turned off "per connection randomized MAC" and enabled "Use Device MAC".
Disabled Settings -> Network and Internet -> "Internet connectivity checks"
Sending 1 ping per second to my phone's IPv6 address from my local network router to try and keep it "alive".
Tried various WiFi access point DTIM interval values (1, 2, 5, 10)

My IPv6 settings in dnsmasq.conf (dnsmasq provides my IPv6 RA service) are as follows

# Turn on IPv6 Router advertisements
enable ra
# Use an RA priority of high, RA Interval of 15 seconds and lifetime 9000 seconds
ra-param=br0,high,15,9000
# Only offer IPv6 RA for SLAAC but no DHCPv6 on this segment
dhcp-range=2XXX:XXXX:XXXX:XXXX::, ra-only

Does anyone have any suggestions of what else I can check or try to change?

I really just want to know if someone else has IPv6 on Wifi working so that I can get an idea of whether this is something unique to just me and my environment. If you do have it working then can I get your RA settings and whether you've modified the WiFi DTIM or other settings?

Thanks for your help and advice.