@Elfstones 

Hi, May I know who is your internet service provider?

I see some service providers might use CG-NAT on their networks:

CG-NAT Blocks my OpenVPN and restricks the NAT type

Best regards.

  @David-TP 

Hi, Thanks for the message.

I see the Linksys WRT-1900ACS supports OpenWRT and I think additional configurations might have been done on the Linksys.

And I noticed you mentioned the internet connection type on Deco is PPPOE, most of time, PPPOE could get a public IP address but it seemed like you still get a private one-the 100 ips on IPv4 on Deco. I hope you could check with South Africa's Webafrica to see whether they could provide a public IP address or open the related ports on ISP gateway for Deco X60.

By the way, May I know what you set up TP-Link DDNS for, remotely accessing a local server?

Thank you very much.

Best regards.