MT6000 slows down 5Ghz connection after some time

I am using the latest stable firmware for the MT6000 router. After some time connected, certain devices on the 5GHz band experience reduced speeds. Examples include a GL-AR750s in repeater mode and an Amazon Echo Show 5.

I noticed that initially, they connect using an 80MHz channel width, but after a while, the connection drops to 20MHz on these devices, causing a sharp decrease in download speeds. In the case of the AR750s, the upload speed remains normal. I tested this using both 80MHz and 160MHz channel widths config, always on 11a/n/ac/ax.

Taking AR750s as an example, if the repeater reconnects, will the WiFi speed (From MT6000 -> AR750s) be better?

Will other devices such as cellphones, laptops, and Pads be like this?

Yes, after a reconnection, wifi speed is better, for a while.

Yes, like I said, Amazon Echo show 5 (we can say it's an Android device)

  1. Please let me know the topology figure
  2. Firmware information, closed-source firmware or open-source firmware? Corresponding version number?
  3. Collect the WiFi logs, SSH into the device to capture it from the normal to abnormal process:
    cat /proc/kmsg& logread -f&
  1. Please let me know the topology figure

Using router as PPPoE thru fiber modem.

  1. Firmware information, closed-source firmware or open-source firmware? Corresponding version number?

I tested with closed source firmware 4.6.8 and 4.6.4. Both have the same problem. But... firmware 4.6.2 doesn't have the issue! So it's something that change from firmware 4.6.2 to 4.6.4

  1. Collect the WiFi logs, SSH into the device to capture it from the normal to abnormal process:
    cat /proc/kmsg& logread -f&

When you say device, you mean MT6000?