@Ivaylo Today only got the router and while configuring got fw update. So not sure if hard reset or revert old fw will help. Did you tried this ? It's it working for others or its just me who facing...

@Ivaylo thanks but it will not solve the problem. I am looking for solution not a work around

After getting Firmware update facing wearied issue. When I connect my mobile(OnePlus 7t) to WiFi , it will connect to 5ghz but after some time automatically it's switching to 2.4ghz. not sure why...