@Kostia16384 

I gave up with the QoS years ago, every time I enable it it just seems to play havoc, if your router has it try using airtime fairness.

It's been covered many times before and I think it ends up dancing around the devices spending more time deciding than doing, like traffic lights when they constantly stop the traffic to let the other flow go, it's the time between the changes that slurps up the time and speed of the flow.

  @Bogle thanks! Is it just a TP-link problem, or a general one?

Hi  @Kostia16384,

If QoS rules are not set correctly, it may cause important traffic to be deprioritized, thus affecting overall performance. Please double-check your settings first.

Other possible causes of the problem are as follows:
Traffic monitoring: QoS requires real-time monitoring and management of traffic, which may consume additional processing resources and affect the performance of the router.
Congestion control: In high-traffic situations, QoS may enforce stricter traffic control, resulting in delays and reduced speeds.

Here are some suggestions:
Check the configuration: Double-check the QoS settings to ensure that the priorities and bandwidth limits are correct.
Test different settings: Try adjusting or disabling QoS settings to observe the changes in network performance.