Maybe these links can help you http://www.tp-link.com/en/faq-1239.html http://www.tp-link.com/en/faq-1544.html

You would better contact tplink support

Good news, My friend Rodrigo who have contacted with TP-Link Support Engineer, and the engineer Calvin said to him, they are working on this issue. And they are looking for customer to help them...

It seems that Arhcer C2600 can not disable SIP ALG. I can find it on my Archer C9 (NAT Forwarding -> ALG). If you need disable SIP ALG, you would better contact support@tp-link.com

Thanks for your sharing, I will notice that if my C9_v3 faced the same.

Is there any result of your testing ? TechLoic wrote I'll do the same and see if it fixes it.