@BigRedCustoms 

The Archer C5400X does not support LACP like the business switch.

Is there a alternative link aggregation mode on the modem that is static? For example, balanced XOR should work.

@Tony 

Not that I see off hand, I'm just trying to use the Link Aggregation from the SB8200 (pictured below) to connect to the router via WAN-Aggregation on the WAN port and Port 1 of the router:

Here are it's instructions for the SB8200 modem:

1. Connect the Ethernet cable to the WAN Ethernet port on the Wi-Fi router and to Ethernet port 1 on the back of the SB8200 cable modem.
    
2. Connect a second Ethernet cable to the Link Aggregation Ethernet port on the Wi-Fi router and to Ethernet port 2 on the back of the SB8200 cable modem. 
   
   

 
Enable Link Aggregation 

1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter http://192.168.100.1 into the address box and press the Enter key.  The Connection page will appear.
   
   NOTE: A security or private risk alert may appear on the web browser advising users to proceed with caution when accessing the Web Manager.  There is no risk in proceeding to the Web Manager. For instructions to by-pass the alert screen, refer to article # 18181 - Alert Message for Web Manager Access.
    
2. Click the Advanced link on the main menu.  The Link Aggregation Configuration page will appear. 
    
3. Check mark the Enable LAG box, then click the Apply/Save button.  The pop-up box will appear.
   
   
    
4. Click the OK button to reboot the SB8200.

Then for the Archer c5400X:

4. 6. Set Up WAN Aggregation WAN Aggregation transforms the LAN1 port to an additional WAN port, and makes a single high-bandwidth data path. Unleash faster internet from ISPs that provide bandwidth rates over 1Gbps and no longer be limited by your networking hardware. Note: Before enabling this feature, make sure that your ISP supports WAN Aggregation and your modem has two WAN ports.

1. Visit http://tplinkwifi.net, and log in with your TP-Link ID or the password you set for the router.

2. Go to Advanced > Network > Internet.

3. Toggle on WAN Aggregation to enable it and the router will reboot to apply the settings. 25 Chapter 4 Set Up Internet Connection

4. Connect the router’s WAN port and LAN1 port to your modem’s two WAN ports with two Ethernet cables.

Tony,

Only other thing I might be running into is maybe a network loop when just connecting from the modem to the router during boot up, maybe a good feature to add to the router firmware for these link agg modems or link agg NAS's is maybe a kind of loop detect function or some sort of error correction in the router firmware. I'll try to time my connections and re-connections to ports at different intervals or start-up phases to see if anything changes.

It might explain why the one port is Tx/Rx (indicated by a traffic sensing flashing LED on port 1 on the modem) is fine and the other (port 2) is solid ON, almost looking like constant activity. Again, this only happens with the C5400X router, the switch always works fine with link agg.

I'll do some more work on this tonight. I've also tried both individual ports on the modem in single cable only LAN configs so the ports are good. Any other ideas, I'm all ears!