[RESOLVED] Suddenly clients not getting IPv6 address

OpenWrt Version - 24.10.5
My Setup - A gpon modem from ISP where fiber is terminated and OpenWrt router WAN port is connected to gpon modem lan port.

I have a cron setup to restart gpon modem everyday at 5:00 AM (I found this helps to maintain internet speed). Today after the reboot, none of the clients connected to OpenWrt router got IPv6 address.

OpenWrt network config as below,

root@OpenWrtTcr:~# cat /etc/config/network 

config interface 'loopback'
        option device 'lo'
        option proto 'static'
        option ipaddr '127.0.0.1'
        option netmask '255.0.0.0'

config globals 'globals'
        option ula_prefix 'fdb9:878a:694f::/48'
        option packet_steering '1'

config device
        option name 'br-lan'
        option type 'bridge'
        list ports 'lan1'
        list ports 'lan2'
        list ports 'lan3'

config interface 'lan'
        option device 'br-lan'
        option proto 'static'
        option ipaddr '192.168.1.1'
        option netmask '255.255.255.0'
        option ip6assign '60'

config interface 'wan'
        option device 'wan'
        option proto 'pppoe'
        option username 'xxx@ftth.bsnl.in'
        option password 'xx'

config interface 'wan6'
        option device 'wan'
        option proto 'dhcpv6'

config interface 'modem'
        option proto 'static'
        option device 'wan'
        option ipaddr '192.168.20.2'
        option netmask '255.255.255.0'

Currently Interface tab screenshot seen as below,

Issue was at ISP end, after they fix it I see IPv6-PD being assigned on wan_6 interface