Hi,
Sorry for my late reply; not evident during work hours. The same problem occurs if I restart the network service. Below the output of the requested commands after the router reboots.
The same commands executed in a working configuration reveal the route from wan6 to to the ISP modem which is found to be missing after the reboot (default via 2a01:e35:87xx:yyy0::1 dev eth0.2 metric 1024). However this route appears in Luci. Your help is appreciated.
root@OpenWrt:~# ip -4 a; ip -4 r
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1000
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
5: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
inet 192.168.1.1/24 brd 192.168.1.255 scope global br-lan
valid_lft forever preferred_lft forever
7: eth0.2@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
inet 192.168.61.156/24 brd 192.168.61.255 scope global eth0.2
valid_lft forever preferred_lft forever
default via 192.168.61.1 dev eth0.2 src 192.168.61.156
192.168.1.0/24 dev br-lan scope link src 192.168.1.1
192.168.61.0/24 dev eth0.2 scope link src 192.168.61.156
root@OpenWrt:~# ip -6 a; ip -6 r
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
inet6 fe80::7aa3:51ff:fe44:ce86/64 scope link
valid_lft forever preferred_lft forever
5: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2a01:e35:87xx:yyy1::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::7aa3:51ff:fe44:ce86/64 scope link
valid_lft forever preferred_lft forever
7: eth0.2@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2a01:e35:87xx:yyy0::c2b0:adbf/128 scope global dynamic
valid_lft 85508sec preferred_lft 85508sec
inet6 fe80::7aa3:51ff:fe44:ce87/64 scope link
valid_lft forever preferred_lft forever
8: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 fe80::7aa3:51ff:fe44:ce84/64 scope link
valid_lft forever preferred_lft forever
9: wlan1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 fe80::7aa3:51ff:fe44:ce85/64 scope link
valid_lft forever preferred_lft forever
default from 2a01:e35:87xx:yyy0::c2b0:adbf via fe80::f6ca:e5ff:fe5a:694a dev eth0.2 metric 512
2a01:e35:87xx:yyy0::/64 dev eth0.2 metric 256
2a01:e35:87xx:yyy1::/64 dev br-lan metric 1024
unreachable 2a01:e35:87xx:yyy1::/64 dev lo metric 2147483647 error -148
fe80::/64 dev eth0 metric 256
fe80::/64 dev eth0.2 metric 256
fe80::/64 dev br-lan metric 256
fe80::/64 dev wlan1 metric 256
fe80::/64 dev wlan0 metric 256
anycast 2a01:e35:87xx:yyy1:: dev br-lan metric 0
anycast fe80:: dev eth0 metric 0
anycast fe80:: dev eth0.2 metric 0
anycast fe80:: dev br-lan metric 0
anycast fe80:: dev wlan1 metric 0
anycast fe80:: dev wlan0 metric 0
ff00::/8 dev eth0 metric 256
ff00::/8 dev eth0.2 metric 256
ff00::/8 dev br-lan metric 256
ff00::/8 dev wlan1 metric 256
ff00::/8 dev wlan0 metric 256
root@OpenWrt:~# uci show network
network.loopback=interface
network.loopback.ifname='lo'
network.loopback.proto='static'
network.loopback.ipaddr='127.0.0.1'
network.loopback.netmask='255.0.0.0'
network.globals=globals
network.globals.ula_prefix='fd24:5b4d:bfc0::'
network.lan=interface
network.lan.type='bridge'
network.lan.ifname='eth0.1'
network.lan.proto='static'
network.lan.ipaddr='192.168.1.1'
network.lan.netmask='255.255.255.0'
network.lan.ip6assign='64'
network.lan_dev=device
network.lan_dev.name='eth0.1'
network.lan_dev.macaddr='78:a3:51:44:ce:86'
network.wan=interface
network.wan.ifname='eth0.2'
network.wan.proto='dhcp'
network.wan_dev=device
network.wan_dev.name='eth0.2'
network.wan_dev.macaddr='78:a3:51:44:ce:87'
network.wan6=interface
network.wan6.ifname='eth0.2'
network.wan6.proto='dhcpv6'
network.wan6.reqaddress='try'
network.wan6.reqprefix='auto'
network.wan6.ip6prefix='2a01:e35:87xx:yyy1::/64'
network.@switch[0]=switch
network.@switch[0].name='switch0'
network.@switch[0].reset='1'
network.@switch[0].enable_vlan='1'
network.@switch_vlan[0]=switch_vlan
network.@switch_vlan[0].device='switch0'
network.@switch_vlan[0].vlan='1'
network.@switch_vlan[0].ports='0 1 2 3 6t'
network.@switch_vlan[1]=switch_vlan
network.@switch_vlan[1].device='switch0'
network.@switch_vlan[1].vlan='2'
network.@switch_vlan[1].ports='4 6t'
network.@route6[0]=route6
network.@route6[0].interface='wan6'
network.@route6[0].target='::/0'
network.@route6[0].gateway='2a01:e35:87xx:yyy0::1'
network.@route6[1]=route6
network.@route6[1].interface='lan'
network.@route6[1].target='2a01:e35:87xx:yyy1::/64'
root@OpenWrt:~# uci show dhcp
dhcp.@dnsmasq[0]=dnsmasq
dhcp.@dnsmasq[0].domainneeded='1'
dhcp.@dnsmasq[0].boguspriv='1'
dhcp.@dnsmasq[0].filterwin2k='0'
dhcp.@dnsmasq[0].localise_queries='1'
dhcp.@dnsmasq[0].rebind_protection='1'
dhcp.@dnsmasq[0].rebind_localhost='1'
dhcp.@dnsmasq[0].local='/lan/'
dhcp.@dnsmasq[0].domain='lan'
dhcp.@dnsmasq[0].expandhosts='1'
dhcp.@dnsmasq[0].nonegcache='0'
dhcp.@dnsmasq[0].authoritative='1'
dhcp.@dnsmasq[0].readethers='1'
dhcp.@dnsmasq[0].leasefile='/tmp/dhcp.leases'
dhcp.@dnsmasq[0].resolvfile='/tmp/resolv.conf.auto'
dhcp.@dnsmasq[0].nonwildcard='1'
dhcp.@dnsmasq[0].localservice='1'
dhcp.lan=dhcp
dhcp.lan.interface='lan'
dhcp.lan.start='100'
dhcp.lan.limit='150'
dhcp.lan.leasetime='12h'
dhcp.lan.ra='server'
dhcp.lan.ra_default='1'
dhcp.wan=dhcp
dhcp.wan.interface='wan'
dhcp.wan.ignore='1'
dhcp.odhcpd=odhcpd
dhcp.odhcpd.maindhcp='0'
dhcp.odhcpd.leasefile='/tmp/hosts/odhcpd'
dhcp.odhcpd.leasetrigger='/usr/sbin/odhcpd-update'
dhcp.odhcpd.loglevel='4'
dhcp.family=tag
dhcp.family.dhcp_option='6,185.228.168.168,185.228.168.169'
dhcp.@host[0]=host
dhcp.@host[0].name='ipad_mini'
dhcp.@host[0].mac='a8:86:dd:b6:d2:6a'
dhcp.@host[0].tag='family'
dhcp.@host[1]=host
dhcp.@host[1].name='lenovo_x1'
dhcp.@host[1].mac='00:24:d7:ce:4e:b0'
dhcp.@host[1].tag='family'