Dear  @RizalAdlink 

There are many factors that may cause this issue. You may check the following steps:

1. The Client PC may saved a wrong password of ths SSID;

2. The nearest EAP has so many clients connected and it can not handle more;

3. The nearest EAP has disconnected from your main network(Ethernet cable connecton issue);

4. There could be Band Steering enabled on the EAP so the nearest EAP won't allow more devices to connect. 

Something you may try:

1. Set up a test 5Ghz SSID, with no password. Then check if your laptop can connect it;

2. Mare sure all EAPs are "connected" status on Omada Controller;

3. Disable Band Steering or Load Balance function 

  @RizalAdlink 

Hi, i have also been having problems with some hardware not connecting or refusing to using the 5G band. I have 3 x eap653, 2 wired and 1 meshed. Channel 40 and 48 i use. The 2G i haven't had any problems with. The item that refuse to connect to the 5G are TP-link ArcherT2U AC600 USB. I also have a TP-Link TL-WA1202 which i was using before upgrading to the 3 x EAP653's and these items connect to that no problem. There is no band steering options on the Omada and the 802.11r roaming feature doesn't seem to work either. Removing the 2Ghz band and it connects.