Tether server on Modem only allow one user to access at the same time.
I guess your Tether client cut down the connection without telling Archer 3200. So Archer 3200 didn't release this client, and you can't access it next time. And reboot the modem can solve this problem, as you say.
It is just a guess....are you change default LAN IP through Tether?

I actually had the same problem, seems to be related to the password. I upgraded to a beta fw and now it works or just try to change the password to something very simple just to confirm that its a password issue.

Where did you got the beta file?

enginolo wrote

I actually had the same problem, seems to be related to the password. I upgraded to a beta fw and now it works or just try to change the password to something very simple just to confirm that its a password issue.

Weber did you got the beta upgrade?

hader wrote

Weber did you got the beta upgrade?

http://static.tp-link.com/Archer_C3200v1_0.9.1_0.1_up_boot(161115)_EUBeta01_2016-11-15_09.42.01_1479451747896g.zip

Thank you it worked but can I trust in beta?? ;)

Will this work for USA version? I am facing the same problem. The router log shows this error whenever tether app tries to connect

2017-01-18 10:45:23

IGMP

Warning

V2 igmp router occured! Not matching ours V3.

I had a similar problem. Though the Tether app would find my router, it would not connect. It gave me an error, indicating that the connection is 'unstable' or that I was connected to a guest network, which was not the case. After contacting support, I understand that the Tether app will only connect if you did not change the default IP-address of the router (192.168.0.1). I changed the IP-address to one in the 10.0.0.x range, as my previous router defaulted to that IP range and have various devices set up with fixed IP addresses in the 10-range. Changing the routers IP address to its default IP address indeed made the Tether app work. However this is not a real solution for those uses that choose to or must use another than the default IP-address / IP-range. I hope the next version of the tether app will allow you to manually configure the IP-address it should connect on.

Atualização para versão beta funcionou e o APP Tether está OK em meu iOS / iPhone

Baixei o firmeware no link abaixo:
https://www.tp-link.com/br/faq-1579.html

Até agora não tive nenhum outro tipo de problema, mesmo sendo versão beta do firmeware.

Tenho vários dispositivos, incluindo interruptores wi-fi, tomadas wi-fi, tv, ipad, iphones e tudo mais.