@Kevin_Z i've try it doesn't work. Any other setting i need to take note??? The speed still drop from 40-50% after few hour usage.

@Leonlay 

I just bought a new router (Asus AX11000)

Now I don't have any problems anymore and my internet is how it's supposed to be 1gbps down and 1gbps up

No tp-link for me

@EonaCat 

If you don't use wired connections and only use wifi then you should be fine. I went the same route but much earlier than you. After I gave up on my Archer AC5400X, then bought an Archer AX11000 and then later Asus GT-AX11000. Now both AX routers are giving me same headache : "Port 1 and Port 2 LAN speed are capped at 100 mbps, while my fiber optic plan should be with 1Gbps speed". The wifi functions work brilliantly in contrast. Regardless how many times i factory reset both units and ensured the firmware are most updated. I was surprised both brands are having same problems and both manufacturers seem not making firmware updates anymore ? I was forced to go back to the Actiontec wifi 5 router supplied by my ISP for my wired gears and bridged port 1 for my Asus GT-AX11000 for wifi only. 

Well ... Tough luck with these high tech gaming routers ! I give up ....

@LarryMan 

For now it works flawlessly with the ax11000.

Too bad that these firmwares give so much trouble

@Milobar 

@EonaCat 

My Asus GT-AX11000 was like yours working well for the first month then problem started ... Also i forgot to mention that the current firmware has a glitch and makes the 5G2 band cannot be set to 160 mhz speed (maxed out on 80mhz) and many users have been experiencing the same issues. This problem is with the PC desktop version of the wifi control, but you won't notice the issue with your phone control app. Unfortunately Asus tech team doesn't care. 

@EonaCat 

Sad case. No QC test properly b4 release to market... customer tonsuffer now. 

I've got the same problem here, I'm running on a restart schedule to mitigate the issue!

Why tp-link doesn't care? Everyone should just return this product

@renatomefi this means they dont care after service. I regret giving them 2nd chqnce and purchase their product.

Previously i use to be like urs set for schedule reboot everyday but issue is aome of my devices cant establish wifi connection after reboot. I.e cctv and so on.

But now i got beta firmware from some one and is fix the issue just they disable the HomeCare feature... ie. Parentcontrol. I have to accept with this limitation no other choice since tplink dont wanna fix it. 

Save some money and go asus layer.

I have the C5400 v2 with the latest stable firmware, 1.2.5 Build 20190411 rel.52981(5553).  I had to go into the QoS section of the Advanced tab on the home page of the router setting menu to manually edit the Total Bandwidth entry to 900 Mbps down and 20 Mbps up for my supposedly 600mbps Xfinity service.  At the wall of the house it was around 880 and at the modem it was around 680 or so.  Now, I get anywhere from 620 to 690.  No beta firmware required. 

There is a button on the Basic tab of the Network Map page named Speed Test.  When I tested, it would register no more than 315/12 and that is what showed up automatically in the Total Bandwidth entry in both the QoS  Application Priority page and Device Priority page.  When I manually edited the QoS Application Priority page entry to 900/20, the bandwidth restriction to both my wired and wireless devices went away.  It also automatically changed the entry in the QoS Device Priority page to match so that I didn't have to make duplicate entries. 

Hope this helps...