@Anh_Alan22 

Possible reasons:

1. WiFi cannot provide a stable environment for Controller to broadcast and discover the EAP

2. Your WiFi is distributing different IPs to EAP and your computer. Omada Controller discovers by the same LAN broadcast.

(precondition is that your switch is a dummy one. If you have something configured to separate the network(e.g. guest network on your WiFi router??), you'll run into issues. The Omada controller discovers based on the reason 2..

  @John1234 : so if you are sure tplink design controller to discover eap on its LAN only, not Wireless LAN( although it in the same subnet), so I have no way to run my pc (where controller is installed). So the pc must near the switch, or connected to the switch by wire. I dont know why tplink scare that wifi is not stabled for discovery, if wifi fails sometimes, we can reconnect the controller. 

My switch is in the basement, so i must install cable to the PC which is on floor 2th, can not use wifi for the PC. 

  @Anh_Alan22 

It works with the WIFI but it is not that stable. (I mean your PC). There is a technology for WiFi that when there is not active traffic, your PC will save power and put in sleep mode or power-saving mode. That actually disconnects the WiFI connection. It is not about the Controller, it's your PC/WiFi settings. So, windows power management will have different settings for you. Do you check them and make sure your PC's never off/sleeping?

It is not TP-LINK scared by that. If you want it to run in a stable network, you'd better make it wired. Anyway, wired is always better than wireless in my opinion. You can consider getting an OC200 or get a raspberry pi and install Linux Controller on it. (Ever since the crypto mining went viral, the raspberry pi's getting more expensive now)

PS found this on EAP. It's something that saves power of the client. Devices> AP> Config> Advanced or you can read the User Guide for the detailed explanation. 

Unscheduled Automatic Power Save Delivery.