You have forgotten add "in my opinion".

Sorry I don't have this router here and I can't check it. Maybe it is some bug in firmware. My advice, you have to contact with TP-Link support and ask about it because I can see this bug first time.

I can see that you have internet access by WAN port. Can you show us this error after GMT button click?

Give us screenshot from Status tab of your router.

Those are two different ADSL modems and we can't compare their. Maybe Billion Bipac 7800N is better for more noisy telephone line.

[QUOTEI don't think WR841HP is powerful enough to cover 120M square][/QUOTE] The same from my side.