Here's what you need to do:
1) Watch my video on proper configs:
https://www.youtube.com/watch?v=qikbVRCRJBw2) Ensure you have the latest firmware on your router and your phone..
3) Under the router's professional Wifi settings disable "Roaming assistant" for your 6 band.
4) On your phone under advanced Wifi settings disable Wifi power savings mode. Disable switch to mobile data when Wifi is weak. Look under Wifi control history to see any apps on your phone have disabled Wifi. Sometimes power management or optimization apps will disable Wifi automatically.
5) Use Wifi Radar on your router to scan for interference and capacity issues across your 2.4, 5, and 6GHz bands. Adjust your control channels accordingly.
6) Enable pre-emptive Bluetooth Coexistence under the 2.4Ghz professional settings
Note that 6e is POWER intensive and your phone's OS/Firmware may simply disconnect in an effort to conserve power. Normally, you can control this, but on some phones you might not have the option. So if you perform all of the above steps and you still have the issue then it's by design and it's specific to your phone, not the router.
Motherboard: ASUS ROG Rampage V Edition 10
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