have you tried this one? http://www.tp-link.com.au/download/Archer-C7.html#Utility( for mac 10.12) if it is the same, it's suggested to submit a ticket to TP-Link support.

try contact TP-LINK support and see what suggestion they will provide

what security option on the main router? WPA-psk? try other security options. If no changes, it is suggested to contact TP-LINK support, someone will follow your case.

we can replace the antenna but should replace all three of them so it will make an difference. And RE580D has 3 external dual band antennas, which means we have to use dual band antennas to do it.

have you seen this before? http://www.tp-link.com/en/faq-547.html And i think if the connection is good and stable, there is no need to take those errors seriously.

hi, does this router get an wan ip address from the ISP? what it is?