@Milobar 

I have the exact issue on my C5400 v2 as everyone else.  The drop seem to happy in hours after the restart.  I have tried to disable QoS and AV but it stays slow.  Wired ports have no issue what so ever.  After 2years, I am thinking to upgrade to the latest AX11000 but seeing this trend even on AX50 is concerning.  I might have to switch to other brand sorry if TPlink is not going to fix this problem.  I can see many unhappy customers here and it will be soon many more if no one in TPlink is taking this seriously.  Sad.

@Milobar i got same problem. Loaded with their beta firmware but still the same. Any solution from u?

@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