@lexlopz 

Before focusing on the A7, connect a computer to one of the LAN ports of the A7 to see what speed it gets. Since it is wired to the modem it should be close to what you get if you were wired directly to the modem.

The 5Ghz band is very susceptable to interference from objects and other 5Ghz signal. 

A couple of recommendations would be to disable the 5GHz on the modem, you would do that to the TP-Link just to test each one like you did in your original post.

Another recommendation would be to modify the wireless channel and width in the TP-Link router to see if you get better performance. Log into the A7, and go to Advanced > Wireless > Wireless Settings > Click on the 5GHz on the top right, and change the values (ex. Channel 36 / Width 80 MHz). You can keep try different combinations to see if any help.

@Tony 

I did what you asked and tested the connection speed via ethernet to both the modem and the router. From the screen shot, the test results from bottom to top are Modem Ethernet, Router Ethernet, Modem Wifi, and Router Wifi. The wifi connections were on the 5ghz band. So you can see that whether it is connected via wifi or ethernet, the internet connection is slower through the router. I did each speed test from the same server as well.

@lexlopz 

Thank you for the information.

Try to disable QoS (Advanced > QoS), and also try disabling NAT Boost (Advanced > System Tools > System Parameters).

Stick with the wired connection for speed testing.