Are you using the guest network for visitors ?

From Kevin's screenshot is not clear that both bands have to be modified if you are not using Smart Connect feature.

Did you set these security parameters for both 2.4GHz & 5Ghz bands ?

@Rafat Yes, you don't have to use an extra HW to achieve that. That's why I asked if you can switch ports or cabling. But then again you can't negotiate more than 10 mbps directly. Refer back to my...

It's just not implemented. In most of the cases auto-sensing would do the job. Try the action from my previous post and see if that helps.

With different router the internet speed is normal, right ? Do a hard reset (Method 1) of the device and re-configure from scratch. If the issue persists then maybe you have a case of incompatible...