Wifi signal dropping every few minutes

Hi,

I have finally managed to set up a hotspot network at my home office.
Using hex S & tenda nova mw3 (3 nodes).

I already set a user profile for special users. This special user, I want the connection to stay alive even though PC is restarted, or mobile phone is put in on/off/standby state.
So I set "KeepAlive Timeout to “1d 12:00:00”, and MAC Cookie Timeout to “3d 00:00:00”.

I don’t see any problem at all with the stability of the connections from my PC. After login page, connections stay alive, even after I restarted the PC.

However, wifi signals that is going to my phones or iPad, keeps dropping every few minutes.
What could have caused this? Are there anything in the settings that I missed?
Should I enable “MAC Cookie” and “Cookie” in “Login by” at Hotspot Server Profile configuration?

Please help.
There must be something I am doing wrong.