Hi  @Hainh 

Please check if you have stable connection on wired network. You can connect a PC to the switch directly to confirm it.

If the wired connection is stable, for wireless client devices, please try to disable 802.11r.(Controller->Settings->Wireless network->WLAN->Edit->Advanced settings->disable 802.11r)

Hainh wrote

My network is as follows:
- (ISP) -> GPON Terminal XZ000-G3 -> ER605 v2.0 -> SG2210P v5.20 -> EAP245(US) v3.0 + EAP620 HD(US) v3.0 + OC200 . divided into 2 wlan: shared network and network for iot devices.
With about 50 phone, laptop, iPad, watch devices, 10 IOT devices for smarthome, 2 security cameras.
 I have a problem with the wifi network: mobile devices often lose connection to the internet (must turn off wifi on mobile and then turn it back on) for about 1-3 minutes.
Has anyone had a similar problem or discovered anything unreasonable? Please help me!

Hi  @Woj-Tech 

There are so many factors that can lead to wireless connection issue. You may refer to 

Troubleshooting of Wireless Issues for Omada EAP Products