Cannot connect using OpenWRT Linksys WRT1900ACS with Spark

I'm hoping that someone has some insight into a problem I'm having with connecting to Spark Fibre using a Linksys WRT1900ACS running OpenWRT.

As far as I can tell I'm tagging the WAN traffic properly but no matter what I try it seems to keep timing out during the PPPoE PADI Discovery step as per this log:

Sat May 16 19:39:00 2020 daemon.notice netifd: Interface 'wan' is now down

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.094493] IPv6: ADDRCONF(NETDEV_UP): eth1.10: link is not ready

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.155163] mvneta f1070000.ethernet eth1: Link is Down

Sat May 16 19:39:00 2020 daemon.notice netifd: Interface 'wan' is disabled

Sat May 16 19:39:00 2020 daemon.notice netifd: Interface 'wan' is enabled

Sat May 16 19:39:00 2020 daemon.notice netifd: Interface 'wan' is setting up now

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.166592] mvneta f1070000.ethernet eth1: configuring for fixed/rgmii-id link mode

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.174409] IPv6: ADDRCONF(NETDEV_UP): eth1: link is not ready

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.180349] mvneta f1070000.ethernet eth1: Link is Up - 1Gbps/Full - flow control off

Sat May 16 19:39:00 2020 daemon.err insmod: module is already loaded - slhc

Sat May 16 19:39:00 2020 kern.info kernel: [ 4009.189421] IPv6: ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready

Sat May 16 19:39:00 2020 daemon.err insmod: module is already loaded - ppp_generic

Sat May 16 19:39:00 2020 daemon.err insmod: module is already loaded - pppox

Sat May 16 19:39:00 2020 daemon.err insmod: module is already loaded - pppoe

Sat May 16 19:39:00 2020 daemon.info pppd[3791]: Plugin rp-pppoe.so loaded.

Sat May 16 19:39:00 2020 daemon.info pppd[3791]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.7

Sat May 16 19:39:00 2020 daemon.notice pppd[3791]: pppd 2.4.7 started by root, uid 0

Sat May 16 19:39:01 2020 daemon.debug pppd[3791]: Send PPPOE Discovery V1T1 PADI session 0x0 length 12

Sat May 16 19:39:01 2020 daemon.debug pppd[3791]: dst ff:ff:ff:ff:ff:ff src 60:38:e0:0b:b9:0f

Sat May 16 19:39:01 2020 daemon.debug pppd[3791]: [service-name] [host-uniq cf 0e 00 00]

Sat May 16 19:39:06 2020 daemon.debug pppd[3791]: Send PPPOE Discovery V1T1 PADI session 0x0 length 12

Sat May 16 19:39:06 2020 daemon.debug pppd[3791]: dst ff:ff:ff:ff:ff:ff src 60:38:e0:0b:b9:0f

Sat May 16 19:39:06 2020 daemon.debug pppd[3791]: [service-name] [host-uniq cf 0e 00 00]

Sat May 16 19:39:11 2020 daemon.debug pppd[3791]: Send PPPOE Discovery V1T1 PADI session 0x0 length 12

Sat May 16 19:39:11 2020 daemon.debug pppd[3791]: dst ff:ff:ff:ff:ff:ff src 60:38:e0:0b:b9:0f

Sat May 16 19:39:11 2020 daemon.debug pppd[3791]: [service-name] [host-uniq cf 0e 00 00]

Sat May 16 19:39:16 2020 daemon.warn pppd[3791]: Timeout waiting for PADO packets

Sat May 16 19:39:16 2020 daemon.err pppd[3791]: Unable to complete PPPoE Discovery

Sat May 16 19:39:16 2020 daemon.info pppd[3791]: Exit.

This is the config I've tried (amongst others):

config interface 'wan'

option ifname 'eth1.10'

option proto 'pppoe'

option password 'password'

option ipv6 '0'

option username 'user@spark.co.nz'

option pppd_options 'debug'

config switch

option name 'switch0'

option reset '1'

option enable_vlan '1'

config switch_vlan

option device 'switch0'

option vlan '1'

option ports '0 1 2 3 5t'

config switch_vlan

option device 'switch0'

option vlan '10'

option ports '4t 6'

Stock firmware on the Linksys had no issues connecting and the Spark HG659b that I'm using as a backup is fine too.

To say I'm at a loss as to what I'm missing would be an understatement so any help would be most appreciated :)