Firmware version 4.6.4
From a cold boot, PPPoE repeatedly fails to connect, rebooting does not fix it.
The only solution is to go to Modify and click Save, the PPPoE connection then comes up immediately.
FTTP ONT is a 2.5GB Nokia ONT, cable has been replaced with a brand new network cable, connection is secure, seems a software issue with saved credentials.
May you please reboot your router, wait 1-2 minutes (so it does not connect PPPoE) and then connect by manually clicking save - after that please export the logs.
According to the syslog, it was not related to the PPPoE program, probably is the port negotiation rate (compatible) issue of the ONT to Brume2, which could prevent the Brume2 WAN up.
Please try to replace the new/high quality network cable.
If no luck, try to set the second LAN port as WAN, to see if it is compatible issue of the 2.5G port. Do them in the SSH:
uci set network.@device[2].name='eth1'
uci set network.wan.device='eth1'
uci set network.@device[0].ports='eth0'
uci set network.@device[1].name='eth0'
uci set board_special.network.wan='eth1'
uci set board_special.network.lan='eth0'
uci commit network
uci commit board_special
reboot