@alexandremq 

Tracking, I had forgot the router has a VPN server and client, even though I have it setup I rarely use it. 

The only way to solve this is by isolating and getting down to the basics. When you test you stil have the client installed i assume. 

Do this and see what results you get. Also keep in mind using the browser as a datapoint is not the best with external source for speed testing you LAN. 

If you really want to get to the bottom of this, you have to isolate further and begin with a known baseline:

1. Hard reset, do not soft reset, you have to phyically hard reset the router and start from scratch to rule out FW/HW or some other backdoor in RAM possibly since you can use 3rd party FW b/c of Broadcom chipset. 

2. Load the latest FW from local drive 

3. Repeat step 1

4. Minimum configuration to connect to your ISP, LAN DHCP IP configuration & Wifi setup. Disable ALL other Router configuration options including anything VPN related.

5. On your Windows machine, remove any and all VPN clients. If you have a new machine reimaged that would be best. Your variablity is on the client end at this point

6. Download and install inSSIDER or TamoSoft throughput tester (On Windows machine)

7. Sitting Next to the Router or in the same room. Test and what see the throughput is 

8. Install NordVPN client on machine and retest in the same location. 

Curious to see what the results are

  @AXE16000_A 

One thing I didn't mention and to be honest I didn't see any difference so far, was about removing the ISP moden/router to use directly an ONT and then have the tplink router configured with PPPoE from ISP as well as IPTV / VLAN 

However as said, I didn't notice any difference so far from when I was using the ISP moden/router or as for now with the ONT

When I did that config to use ONT, around 2 weeks ago, I needed to do a factory reset and start from scratch config everything. I was already using the last FW version for my tplink router. 

However I didn't do exactly the way you described. After I finished the config of ONT + my router, I already got the same speed as ISP moden/router. That was before installing anything about VPN. So, to be honest I am not completely sure if steps you mentioned will have any impact, but I also want to try.

I can do that only during the weekend and also on that I cannot use the windows laptop as that is a company property I use only to work. Tests I did with that laptop was before connection with company's VPN, but cannot keep doing or installing anything on that laptop. So my tests needs to be in my mac.

I will reply back here once I am able to do again exactly as you said.  

  @alexandremq 

I agree it should not matter if you have the ISP modem/router in the loop or not. 

The issue you are having if it is an issue is on the LAN side.

If you really want to isolate it test it without the internet in the loop and WAN connection all together. 

To isolate the root cause you might have to go through multiple COA to peel that onion. Broadcom doesn't give you as much access but you can isoalte the wifi band internally first.

You need a fresh asset on the client side, if you use your Mac or phone without knowing what SW/Apps are installed you might be introducing a common problem across those platforms which is why I suggested a fresh imaged OS. Understand your limitation on the work asset, will have to do your best with what you have. I'm not sure if the apps i recommended work on Mac however. There is likely some other 3rd party tools which do the same. 

If you have an android phone there is a couple i can recommend, but always best to start with baseline and test from there otherwise you are chasing a needle in a haystack. 

Hi  @AXE16000_A 

Sorry for the late reply about this. I have done some more investigation, but I confess they didn't go the way you tried to help.

In the end, all my investigations and also your help, my only conclusion was a problem about my ISP.

So I took a different route and switched my ISP. After that everything came back to normal about my router. Download/upload simetric and no more problems at least so far even through the 6ghz band.

To achieve that I didn't do anything else special. As I switched the ISP, I didn't need the ONT any longer. For now I will keep using the moden from this new ISP and lets see if I will continue with the same 1Gb after some months.

thanks for the help! 

  @alexandremq 

Glad you resolved the issue. The good news is your router is just fine and not the issue which was the primary hypothesis.