Sorry no one has an answer for you. If you check the thread again, I was wondering where the setting to turn off AX for the 2.4 GHz network was..?
Would you think the other devices on the 2.4 network would be taking up all the bandwidth? The 2.4 GHz is a different frequency range and may be affected by such things as wireless phones. You are running the 2.4 as 20/40 MHz and you should be getting the full speed. You might watch for time of day or your environment to see if you can find anything in common when the speed is low or high..
The situation with a Bandwidth manager may be a little difficult to understand. Since it prioritizes certain streams, it may limit others so such things as video and gaming get as much as they can. The Speed test may not be set to get any priority.
Maximus Z790 Hero,
Intel i9-13900k
Intel BE200