@Sevi 

I confirm it's a problem with the QOS
Dsabled it and it worked correctly
For when a new firmware with the problem resolved?

I've been doing some troubleshooting, trying to understand what influences the problem. I'll share some more info here about what I've found. I removed the Tether app from my Samsung S10+, Factory Restored the router, downgraded then upgraded the firmware, and configured the router with network names, passwords, enabled Smart Connect. After doing this, my Ethernet desktop achieved the full speed of my Internet service (800 down / 18 up). My wireless Samsung S10+ achieved 480 using Ookla, 436/18 using M-Lab, on the Chrome app. Xfinity app achieved 436/18. My daughter's iPhone XR achieved 429 using Ookla, 363/18 using M-Lab, on the Safari app. It seems my wireless speeds are still roughly 50% of my Internet service limits. 

While testing with QoS enabled, you can watch the Real-time Rate on the Device Priority poriton of the QoS page. I had the bandwidth set to 0/0, no priority assigned, and ran a speed test using the S10+ using Ookla. Ookla reports 233 Mbps while the Real-time Rate showed 742 KB/s. Quite a discrepancy there. There's definitely a bug somewhere in the QoS code.

I wish I knew why after a factory reset my wireless devices don't achieve closer to my Internet service limits. I've used a wifi quality app to see if there's interference on my channels and I appear to have good service. My tests have been run at a distance 5 feet from the router.

Anyway, time to go forage for food. Happy Thanksgiving to everyone.

Good news everyone. I started a ticket  [TP-Link Support]-[TKID211122678] Archer AX3000 V1 QoS Bug, Poor Data Speed  several days ago and provided a lot of data from my speed tests and troubleshooting trials. Here's the response from TP-Link:

After talking to our senior engineers, we found that QoS does affect speed. We take this issue very seriously and have fed it back to the R&D department, but for now the temporary solution is that we recommend you turn off this QoS feature, otherwise your speed will be affected by the QoS feature.

Presumably, R&D will solve the problem and issue a new firmware update.

Stay tuned!

@BPC23 By the time the fix and address this issue most of us will have moved on to a new router and made a vow to never touch a TP Link product again. 

It only took 19+ pages and 193+ comments from product owners for them to even acknowledge it. We even had TP Link reps feed us bull$hit Last time I ever buy a TP Link router. I'd rather spend an extra $50 or $100 to get a router that works right. 

@Sevi 

High Hopes! 

Let´s if during 2022 we have a solution for all this router problems.

sold my AX50 and purchased an Asus router. I was not used to get so many updates, smooth and robust usage...  

I will never buy TP router anymore. I also sold that **** and bought Asus which is working perfectly. 

Issue is still occurring even after the September firmware upgrade. Thanks to everyone in the forum who found the Tether app issue, this has tripled my speeds. I still get an extra 200 Mbps when plugged directly into my ISP's ONT though, the wired and wireless interfaces on this router just don't seem actually capable of a full gigabit. I'm broadcasting with 802.11ax, have an 802.11ax card, confirmed the wireless protocol is identified as 802.11ax in Task Manager, but I can't get anything greater than the theoretical maximum of 802.11ac. The link speed on my computer's network adapter fluctuates from 1.2 to 2.4 Gbps, but I can't actually get close to that speed out to the internet through this router. 

I will definitely be replacing this with an Asus, Acer, or even a Linksys would probably perform better. 

I have a different router (AX5400) and I don't even have an option to modify QoS. Accidentally turned it on with the Tether app and set a bandwidth. Now my internet is half speed and I can't change anything, web-based site or app.

@JackMx 

There is no option to totally disable it on any of these unfortunately. Even after all this time, TP-Link has left this bug and done nothing to fix it. I would suggest buying a different router, but you can delete the tether app and factory reset. That's the only way.