@Tunkurman 

Yes mate. I dont understand it either. Support started talking to me via mail to get us off this forum then suddenly stops replying. They have no idea what the issue is is my feeling.

@dmk 

Same to me. They are afraid to answer. They just want us to be quiet in here. I refuse too.

Update, but without success story: they asked me (again) to upgrade router to beta firmware that I already did and I send them feedback, that problem still exists.

They are not even reading emails!!!

@dmk 

hahaha the same guy asked me to do the same. I asked him if it was a joke.

To sum up: after few days support did only one thing: send firmware with beta wallpaper and nothing more. They don't even asked for logs, tryied to figure out problem, do some remote call, anything. They just shared some internal built of firmware with warning that this could void warrenty (that's the most funny part - they have problem, thay can't fix it on warrenty, so they share firmware that could void warranty - f*ck the logic).

To sum up, to everyone who is thinking of buying any tp-link router (Archer AX11000, Archer AX6000, Archer AX1500, Archer AX50, Archer AX20, Archer AX10, Archer A7, Archer C9, Archer C80, Archer C4000, Archer C5400X, Archer C2300, Archer A9, Archer A8, Archer C7, Archer C6U, Archer A6, Archer C6, Archer C1200, Archer C50, Archer A5, Archer C20): don't even think about it! TP-Link doesn't provide you any support or warranty. They have broken firmware and they don't even know where to look for a problem. It's cheap and crap hardware. DO NOT BUY THIS PRODUCTS!!!

@Kevin_Z 

I tagged you in post #20 and provided detailed information hoping for a response but none was provided.

Please provide updates to all of us via this thread given we all appear to be having the same problem and likely root cause.

Further to my previous posts in this thread I can confirm this is definitely a C9 issue rather than an issue with my cable broadband provider or modem as follows:

I hooked up the cable modem to a much cheaper and older router & it  to my C9 (cable modem->old router WAN port->old router LAN port->C9 WAN port), and continued to use C9 for wifi & LAN connections. C9 restarts multiple times a day and during each restart; while all its devices are thus disconnect from the internet,  I can still connect a laptop to the old router via lan or wifi and have internet access.

Have you tryied switch C9 to Access Point mode? I know that this is not a solution but I'm interested if this is problem in router mode, or global problem. As I understand you don't forward all internet traffic to your C9 (using DMZ for example), so this is not attacs comming from the WAN side?