Zeno wrote

Hello , i'm facing issues in C6 v 3.20(us) while downloading files through 5ghz while sitting next to the router, i get around 100-200 KB/s max (while downloading the file) where as in 2.4ghz i get around 4-5 MB/s (not mbps) . I also checked with other laptops same results. My speed on speed test is 300mbps download and upload. Also i have disabled QOS, dos protection and set duplex to 1000mbps. Moreover i check it in my phone and got same results. 2.4 is giving 4/5 MB/s and 5ghz is giving 100-200 KB/s. It's strange.

update :- after using VPN(1.1.1.1) 5ghz  is giving max 10 MB/s. 
any ideas ? What is happening?

Hello @Zeno, what is the device that connects to the 5G network and you are testing the downloading? Is it a computer? You can follow the guide to confirm the link speed between the computer and the router:

https://www.tp-link.com/support/faq/2265/

Are there any special software or applications on the computer? I will suggest disabling those then testing the downloading. Except for the downloading, how about other services, are they also suffering from the slow speed when connecting to the 5G network? Please confirm this with some other 5G clients, such as phones.

Zeno wrote

@Kevin_Z  hello the device which is connected to 5ghz is a laptop. (Acer swift 5, Windows 10) and i checked the link speed it is 866.7 MBps . 
Just the downloading speed is slow. I have disabled firewall on windows. Updated my wifi drivers and in C6 i have disabled dos protection and Qos .

i have tested this on other laptops as well, same downloading speed 10-30kbps and speed test showing 300mbps upload download. 

Phone downloading speed keeps on changing i don't know why, sometimes it gives 6-8MB/ps and sometimes in kbps ! But 2.4ghz is stable at 7-8 MB/ps 

Hello @Zeno, forgot to ask, have you ever tried to reset the router to factory defaults and reconfigure it from scratch? Give it a go and just set up the internet on the router, don't modify or change any advanced settings on the router, then check the downloading again.

BTW, what kind of download you are using? Any website can be referred to? You can try if it helps by changing the DNS server on the router WAN to 8.8.8.8 or 1.1.1.1, then confirm.