IPv6 stops working when LTE is active

I have 2 WAN connections one is PPPoE and the other is QMI (LTE), when it's just the WAN everything is fine but when the WWAN is active with this config:

config interface '4G'
	option proto 'qmi'
	option auth 'none'
	option pdptype 'ipv4v6'
	option device '/dev/cdc-wdm0'
	option metric '50'

IPv6 simply becomes unusable on the router (on devices it's fine I can test using test-ipv6.com), for instance pinging google.com like this:

root@router-box:~# ping google.com
PING google.com (2404:6800:4007:826::200e): 56 data bytes

Ends up with nothing, I noticed in my route output:

root@router-box:~# route -A inet6 | grep '::/0'
::/0                                        ::                                      U     2010   1        0 wgc_Ada 
::/0                                        ::                                      !n    -1     2        0 lo      
::/0                                        2402:3a80:e2c:5d0e:bcf0:a407:d53d:bd0a  UG    50     5        0 wwan0   
::/0                                        fe80::f6bf:a8ff:fe75:1144               UG    512    5        0 pppoe-wan
::/0                                        ::                                      !n    -1     2        0 lo      

(wgc_Ada is a wireguard peer)

Why is the wwan0 route having a lower metric than pppoe-wan even though in /etc/config/network I have set:

config interface 'wan6'
	option device '@wan'
	option metric '10'
	option reqaddress 'try'
	option reqprefix '48'
	option sourcefilter '0'
	option proto 'dhcpv6'

When I turn off the WWAN connection or even just turn it from IPV4V6 PDP type to IPV4, everything works well. Any pointers on how I can resolve this would be appreciated