Help with adding OpenWRT router to T-Mobile Home Internet / IPV6 issues

Hi all, I'm trying to add an OpenWRT router to the T-Mobile Home Internet gateway.

It's mostly working smoothly except IPV6.

I followed the instructions that seem to be the one to follow from a Reddit post here and set WAN6 and LAN to Relay and WAN6 to Master, but I'm getting issues where it will switch between IPV4 and IPV6 intermittently.

I get "your connection was interrupted, the network has just changed" errors when regularly web browsing, and using an IPV6 test site, I'll see that it keeps switching from IPV6 to IPV4, often falling back to just IPV4 only. On my Mac's network settings, I see that the IPV6 address for the router keeps intermittently disappearing and reappearing.

Any help would be appreciated, if there's anything I missed and need to do further to get this to work right. Thanks.

/etc/config/dhcp:

config dhcp 'lan'
	option interface 'lan'
	option start '100'
	option limit '150'
	option leasetime '12h'
	option dhcpv4 'server'
	option ra 'relay'
	option dhcpv6 'relay'
	option ndp 'relay'
	list ra_flags 'none'

config dhcp 'wan'
	option interface 'wan'
	option ignore '1'
	list ra_flags 'none'

config dhcp 'wan6'
	option interface 'wan6'
	option ignore '1'
	option master '1'
	option ra 'relay'
	option dhcpv6 'relay'
	option ndp 'relay'
	list ra_flags 'none'